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As time passes since Hamas’s attack on October 7, 2023, investigations continue to be published, facts clarified, and insights sharpened. Among these is a growing recognition of the deep cognitive fixation that gripped the Israeli Defense Forces (IDF) in the years leading up to the attack—and how it contributed to the military’s lack of preparedness in the face of an evolving threat. This cognitive fixation reinforced a conception of Hamas as a responsible governing entity—one that prioritizes the well-being of its citizens, sought improved economic conditions, and aimed to develop the semi-state entity under its control. This led to the belief that Hamas was interested in maintaining calm, preserving its assets, and solidifying its rule over the Gaza Strip. Over time, this assumption became entrenched as an accurate reflection of reality in Gaza, leading to the self-persuasion that Hamas was deterred from initiating war against Israel. Consequently, key developments in the Gaza arena since 2018 were misinterpreted. Information and warning signals that challenged the conception were dismissed or interpreted as noise. In turn, the conception itself further contributed to reinforcing the cognitive fixation—thus creating a vicious cycle.

This article examines one of the key drivers of cognitive fixation within the IDF’s General Staff: the similarity among decision-makers and policy shapers. This similarity stems from a process of “human replication”—the selection and promotion of individuals who resemble one another—and a clear preference for including such individuals in the inner circle of the IDF’s strategic thinking. This phenomenon is referred to as “similarity bias,” a well-documented cognitive bias that reflects the limits of human imagination in addressing unconventional, extreme, or norm-defying scenarios. In this article, similarity bias is addressed in its behavioral dimension—as a preference in the selection of individuals.

This bias stems from a deeply rooted human, social, and cultural tendency to favor individuals who share similar characteristics—interests, values, appearance, and interpersonal familiarity—particularly in recruitment and promotion contexts. Such tendencies lead to the formation of homogeneous groups and reinforce close-knit ties among individuals with similar views. This dynamic  curtails cognitive diversity and reinforces unchallenged viewpoints. In professional and organizational settings, leaders and commanders who prioritize candidates resembling themselves miss opportunities for critical and innovative thinking. This not only stifles the emergence of new ideas but also reinforces existing assumptions and prejudices, ultimately undermining the group’s ability to consider diverse perspectives and question prevailing beliefs.

Like other cognitive biases, similarity bias has both advantages and disadvantages, depending on the context. It promotes a sense of comfort and belonging, strengthens social bonds, facilitates communication and collaboration, and can enhance loyalty to leaders and their vision. It may also contribute to more rapid decision-making. At the same time, these benefits come at the cost of reduced diversity of thought and experience, which can limit creativity and innovation. Moreover, it can lead to the exclusion and discrimination of individuals who differ from the dominant group, reinforce existing biases, and impair the group’s ability to critically assess new or alternative ideas.

For years, it has been argued that similarity bias is prevalent within the IDF and undermines its performance. One example is the pointed critique of Maj. Gen. Yaniv Asor, who served as head of the IDF’s Personnel Directorate and was compelled to end his military service amid strained relations and deep disagreements with the former Chief of Staff Herzi Halevi. Asor, who was recently appointed  Commander of the Southern Command, used his farewell speech in November 2024 to voice criticism of  the lack of diversity within the General Staff—remarks that were omitted from the IDF’s official press release on the change of leadership. In his speech, Asor emphasized that the majority of recent chiefs of staff and their deputies have come from the Paratroopers Brigade, stating: “Human diversity in every unit, corps, and branch—from the basic training bases to the General Staff—is critical to the success of our missions. Excessive homogeneity carries the risk of cognitive fixation, of tunnel vision. After all, it was entrenched conceptions and blind spots that led to what we are currently facing.”

Despite ongoing discussions about the IDF as an organization and the processes surrounding senior appointments, there remains a lack of in-depth, data-driven analysis of these phenomena. This article, therefore, presents empirical data concerning the prevalence of similarity bias and explores its potential role in generating cognitive fixation. We argue that this fixation contributed to the development of a strategic conception that ultimately enabled the surprise attack of October 7. Accordingly, in light of these findings, and with the appointment of Lt. Gen. Eyal Zamir as the new chief of staff, it is imperative to examine the data and its implications. Organizational reforms are needed to mitigate the effects of similarity bias, including efforts to increase diversity in staffing across the General Staff and command positions in all branches of the IDF, as well as undertaking reform of its promotion processes for commanders.

Senior Appointments in the IDF—Data

The appointment of officers to senior ranks—lieutenant colonel, colonel, and brigadier general—follows a structured process. Placement discussions are held with key decision-makers, either the chief of staff (for brigadier general and colonel appointments) or the relevant major general (for lieutenant colonel appointments), along with other major generals, representatives from the Personnel Directorate, the Behavioral Sciences Department, Staff Division, and additional bodies. Each position has several candidates who are presented with a comprehensive data file that includes scores from an assessment center—conducted by senior reserve officers who do not know the candidate—as well as evaluations by commanders and peer assessments (“sociometric” reviews). While the process for appointing brigadier generals is officially similar (although without an additional assessment center), in practice, such decisions are typically made between the chief of staff and a few major generals. Appointments of major generals are made solely by the chief of staff, following discussions with the defense minister and subject to the minister’s approval. The minister’s approval is also required for the placement and promotion of colonels and brigadier generals, although in many cases, the minister is not familiar with the candidates. This situation creates conditions in which senior officers—among them the chief of staff—may select individuals similar to themselves, demonstrating similarity bias.

To examine the claim of similarity bias in the IDF, we analyzed the originating units of senior officers, based on the assumption that if such a bias exists, certain units would be significantly overrepresented. The positions reviewed included the chief of staff, the head of Military Intelligence Directorate, the commanders of the Northern, Central, and Southern Commands, and the commander of Bahad 1—the IDF Officers’ School. Our sources included official websites, such as that of the IDF spokesperson and other personal and public online information. We excluded individuals who began their military service prior to the establishment of the State of Israel—in the British Army, the Haganah, or the underground organizations. Thus, our dataset spans appointments to these roles over the past fifty years, beginning in the late 1970s with Moshe Levy as chief of staff, Yehoshua Sagi as head of the Military Intelligence Directorate, and Dan Shomron as commander of the Southern Command. Our findings show that all  commanders surveyed came from one of the following units: Paratroopers/Sayeret Matkal, Golani, Armored Corps, Artillery Corps, Intelligence, Air Force, Navy Commando Unit (Shayetet 13), Givati, or Nahal.

Table 1.

Data Summary

• Chief of Staff: From Moshe Levy to Lt. Gen. Eyal Zamir, there have been 13 chiefs of staff. Nine served in the Paratroopers/Sayeret Matkal. Two came from the Golani Brigade (Gabi Ashkenazi and Gadi Eisenkot), one from the Air Force (Dan Halutz), and one from the Armored Corps (Eyal Zamir). All, except Halutz, previously led one of the regional commands.
• Heads of Military Intelligence Directorate: Since Yehoshua Sagi, 13 major generals have led the Military Intelligence Directorate. Of these, seven served in the Paratroopers/Sayeret Matkal (Ehud Barak, Amnon Lipkin-Shahak, Moshe Ya’alon, Aviv Kochavi, Herzi Halevi, Aharon Haliva, and Shlomi Binder), two in the Armored Corps (Amos Malka and Tamir Hayman), one in Golani (Uri Sagi), and one in the Air Force (Amos Yadlin). Only two came from within the Military Intelligence Directorate itself (Yehoshua Sagi and Aharon Zeevi-Farkash). Of all the heads of the Military Intelligence Directorate in the period reviewed, five were later appointed chiefs of staff—all from the Paratroopers/Sayeret Matkal.
• Northern Command: The picture is similar across the regional commands. Since Avigdor (Yanush) Ben-Gal, 15 major generals have led the Northern Command. Seven were from the Paratroopers/Sayeret Matkal, four from the Armored Corps (including Uri Orr and Yossi Peled), three from Golani, and one from Givati (Yoel Strick). Of all Northern Command commanders, four were appointed as chiefs of staff—two from the Paratroopers/Sayeret Matkal (Benny Gantz and Aviv Kochavi) and two from Golani (Gabi Ashkenazi and Gadi Eisenkot).
• Southern Command: Since Dan Shomron, 18 major generals have led the Southern Command. Ten came from the Paratroopers/Sayeret Matkal, five from the Armored Corps, and one each from Golani (Uri Sagi), Shayetet 13 (Yoav Gallant), and the Artillery Corps (Dan Harel). Of the Southern Command commanders, four became chiefs of staff: Three from the Paratroopers (Dan Shomron, Shaul Mofaz, and Herzi Halevi) and one from the Armored Corps (Eyal Zamir).
• Central Command: Since Moshe Levy, 23 major generals have led the Central Command. Fifteen of them came from the Paratroopers/Sayeret Matkal, four from Golani, three from the Armored Corps (Uri Orr, Amram Mitzna, and Avi Mizrahi), and one from Nahal (Yehuda Fuchs). Four of these commanders were later appointed chiefs of staff—all from the Paratroopers (Moshe Levy, Amnon Lipkin-Shahak, Ehud Barak, and Moshe Ya’alon).
• Bahad 1 (IDF Officers School): The most striking figure relates to the commanders of Bahad 1, the IDF’s Officer Training School. Since Zvi Bar’s tenure in 1971, 21 out of 27 commanders have come from the Paratroopers. This figure raises the question of why the tradition of appointing infantry officers to this role persists, despite the fact that Bahad 1 trains officers from all IDF branches. Officers from the Armored Corps, Artillery, and others are equally capable of leading and educating the next generation of commanders.

Another striking data point not included in Table 1 relates to the parent units of the four current or recent heads of Israel’s main security organizations: the former Chief of Staff Herzi Halevi, the Head of the Mossad David (Dedi) Barnea, the Head of the Shin Bet Ronen Bar, and the Head of Military Intelligence Directorate Shlomi Binder—all of whom are alumni of Sayeret Matkal. While it would be difficult to claim that this is a case of “a friend brings a friend,” as these individuals advanced their careers in separate organizations, the shared background further contributes to the discussion on the lack of cognitive diversity.

The emerging picture reveals a pronounced bias in the appointment of senior officers to the General Staff, favoring those who served in the Paratroopers Brigade or Sayeret Matkal.

It is clear that this pattern does not stem from an intentional preference during the initial recruitment or placement at the start of military service to channel the best soldiers specifically to the Paratroopers, with the goal of grooming future General Staff members. Rather, the bias becomes apparent later in an officer’s career, typically at the level of brigade commander and other lieutenant colonel-level positions, where there is a clear preference for promoting officers from the Paratroopers or Sayeret Matkal. The most plausible explanation for this phenomenon is similarity bias. For example, candidates for the role of Paratroopers brigade commander are typically drawn from within the brigade, with four or five officers competing for the position. Those who are not selected often go on to become brigade commanders in other infantry units (Golani, Nahal, Givati, Bahad 1, or the Multidimensional Unit). This is not the case for candidates for the position of Golani or Givati Brigade Commander. Those who are not selected for these roles are usually not promoted to equivalent command positions elsewhere. Moreover, while officers from the Paratroopers Brigade have occasionally been appointed to command the Golani, Nahal, and Givati Brigades, a non-Paratroopers officer has never been appointed to lead the Paratroopers Brigade. The Paratroopers Brigade is undoubtedly an excellent unit—but so are the Armored Corps, the other infantry brigades, the Artillery Corps, and the Military Intelligence Directorate. These all include outstanding officers with the potential to become regional commanders, heads of the Military Intelligence Directorate, or chiefs of staff.

The Problematic Nature of Similarity Bias in General—and in the IDF in Particular

While similarity bias may offer certain advantages—such as prior familiarity and a shared formative background that facilitate a common language and greater agility in decision-making—it poses significant disadvantages within the context of the IDF.

1. Lack of Diversity in Strategic Approaches—Similarity bias may limit strategic diversity, particularly the group’s ability to think “outside the box.” When senior officers prefer team members who resemble them in mindset and approach, tendencies toward groupthink are accelerated and amplified, undermining initiative and creativity. This can lead to suboptimal decisions and insufficient preparedness for unexpected challenges or changes. Moreover, a General Staff composed largely of alumni from elite units—whose operations are typically highly focused and precise—may suffer from narrow thinking.
2. Lack of Diversity in Risk Assessment—This lack of diversity can lead to missed opportunities for innovative and creative crisis management and can limit the organization’s ability to adapt to complex threats or challenges. The group may also fail to assess risks and changes on the battlefield. This effect was clearly demonstrated on October 7 and in the war that followed.
3. Exclusion of Diverse Talents—When senior officers favor individuals who are similar to themselves in background, attitude, or thinking, outstanding candidates who do not belong to the dominant group of policymakers and decision-makers are excluded. Diverse talents bring different thinking, approaches, and creativity that are often absent in homogeneous groups. This lack of diversity undermines equal promotion opportunities and affects the military’s ability to harness the full potential of its personnel. It is hard to believe that the majority of officers suited for the ranks of major general all happened to enlist specifically in the Paratroopers or Sayeret Matkal.
4. Reinforcement of Prejudice and Frustration—The preference for officers with similar characteristics results in biased evaluations—not based on qualifications or capabilities, but on affiliation with certain groups. Beyond harming the overall quality of leadership—since the best candidate is not necessarily chosen—this leads to considerable frustration among others. Since unit affiliation often correlates with socioeconomic background, promotion processes influenced by similarity bias can reinforce perceptions of discrimination and perpetuate social stratification. These effects extend beyond the military, carrying broader social and political implications—including in the political arena. In fact, such bias undermines the military’s historically significant role as a cornerstone of Israel’s melting pot.
5. Limitations on Intra-Organizational Cooperation—When many senior officers come from a shared and narrow background, they naturally tend to collaborate with those similar to themselves while excluding others from key processes. In doing so—often unintentionally—they undermine the potential for effective cooperation within the IDF.
6. Personal Loyalty and Deference to Commanders—In many cases, senior officers appoint individuals who previously served under them. These subordinates often feel a sense of reverence and personal loyalty and commitment toward their former commanders, which may inhibit their willingness to openly disagree or to think subversively—in the positive, creative sense of the term.

Similarity Bias and War Following October 7

It is difficult to avoid asking whether the pronounced similarity bias within the IDF General Staff in 2023 led to—or was among the factors that contributed to—Hamas’s surprise attack on southern Israel on October 7. It should be noted that similarity bias has accompanied the IDF for at least the past fifty years, meaning that the processes that contributed to this traumatic event did not begin under the General Staff led by Lt. Gen. Herzi Halevi. While it is difficult to prove that similarity bias was the cause or a direct factor in the processes that led to the major failure of October 7, it is reasonable to assume that the phenomenon played a role indirectly—primarily by fostering cognitive fixation. This rigidity in thinking allowed a strategic conception to take root, ultimately resulting in blindness and strategic disaster.

Was the prevailing belief within the IDF—that Hamas was deterred, uninterested in conflict, and focused primarily on the welfare of Gaza’s residents—connected to similarity bias? Did the fact that the senior officers responsible for intelligence, situation assessment, and understanding the terrain and enemy all came from similar units limit their thinking, critical judgment, and ability to challenge the prevailing strategic conception? We may never know for sure, but it is evident that their similarity did not help to break through the boundaries of the dominant collective thinking.

The natural question, then, is to what extent similarity bias contributed to the processes the IDF underwent before the war, specifically to the actions and inactions in the days and hours before the war near the Gaza Strip (e.g., at the Nahal Oz outpost), within the Intelligence Corps, and to the unpreparedness of regular and reserve forces. This study did not examine the degree of homogeneity among personnel in Unit 8200 or other intelligence units responsible for early warning. However, it appears that at all levels, the vast majority of personnel share highly similar backgrounds. This raises a further question: Did similarity bias contribute to the uncritical acceptance of the “Hamas is deterred” assumption—and particularly to the failure to amplify the few warnings issued prior to the war, whether in reports, alerts from junior officers, or warnings from female surveillance soldiers stationed on the border? Even those who dispute this direct link cannot entirely dismiss the possibility that similarity bias played a role in reinforcing cognitive fixation.

Recommendations

The data leaves no doubt about the existence of similarity bias within the IDF General Staff in 2023 as well as in the decades preceding it. Given the potential influence of this bias on the strategic conception that contributed to Hamas’s October 7 surprise attack, it would be appropriate for incoming Chief of Staff Lt. Gen. Eyal Zamir to review the findings presented and analyzed in this article and take steps to significantly increase human diversity within the General Staff in particular and in the IDF leadership in general. It is essential that senior positions be filled by officers from various units across the military, including those who bring different ways of thinking, creative approaches based on diverse experiences, operational experiences within different organizational cultures, and distinct leadership styles. Even if the chief of staff chooses to address the issue and take decisive, systematic steps, the change will take time. Moreover, responsibility for reducing the impact of the “a friend brings a friend” phenomenon does not rest solely with the chief of staff; it requires commitment from other actors within the military as well. Success will depend on developing awareness and the ability to recognize the unconscious effects of similarity bias while promoting a culture of open-mindedness and inclusiveness in decision-making.

Among other things, the process for appointing the commander of Bahad 1 should be reviewed. It is worth reconsidering whether only infantry officers should be eligible for this position or whether it should be opened to officers from other branches. Even if the current policy is maintained, it is important that these commanders represent all infantry units rather than predominantly the Paratroopers. Many excellent units exist in the IDF, and a General Staff composed of officers from diverse backgrounds is likely to be a stronger, more effective leadership forum.

To support this process—and others—the establishment of an external oversight mechanism should be considered to review, approve, or participate in the selection process of senior appointments. While it is reasonable for the political echelon to be involved in the appointments of major generals and certain brigadier general roles (such as the head of the Research Division), as is the case with other senior public service appointments, the current relationship between the military and political leadership raises serious concerns about the politicization of the IDF. Any reform in this area must therefore be based on clear and rigorous principles to prevent political interference, which could gravely harm the IDF and its ties with society. Ultimately, any process designed to reduce the harmful effects of similarity bias in the IDF must be conducted thoughtfully and with the utmost care, acknowledging the inherent challenges of eliminating the phenomenon altogether.