You assumed they would react the way you would react. The assumption ran in both directions simultaneously â and both were wrong.
Assumed similarity bias is the tendency to overestimate how similar other people are to oneself in traits, attitudes, or behaviors.
A Scene Worth Recognising
When Maya orders her usual oat-milk latte at the office cafe, she assumes her teammate Alex will also choose the same drink because she enjoys it. She doesn't consider that Alex prefers black coffee and rarely drinks dairy alternatives. Later, Maya is surprised when Alex orders a plain espresso and seems puzzled by her suggestion to share a flavored latte. This moment shows how Maya's own preference acted as an anchor, leading her to overestimate how similar Alex's taste is to hers.
What it means and how it works
The bias arises from egocentric anchoring: one's own traits serve as the default reference point when estimating others' traits. Insufficient adjustment from this anchor, combined with the availability of selfârelated information, results in an inflated perception of similarity.
When judging others, individuals often start from their own characteristics and insufficiently adjust for differences, leading to a belief that others share more of their views, preferences, or habits than they actually do. This bias can affect social perception, decisionâmaking, and interpersonal interactions.
Why it matters
Overestimating similarity can lead to misunderstandings, reduced empathy, and flawed predictions about others' behavior. In contexts such as teamwork, negotiation, or public policy, it may cause conflict, ineffective communication, or misguided assumptions about group consensus.
The verified research on this pattern supports the following:
- People consistently rate strangers as more similar to themselves than objective measures indicate.
- Assumed similarity bias stems from egocentric anchoring where one's own traits serve as the default reference for judging others.
Common misunderstandings
Misunderstanding 1: It is the same as empathy; in fact, it is a cognitive shortcut that can impair accurate understanding of others.
Misunderstanding 2: It only occurs with close friends or family; the bias appears even with strangers or acquaintances.
Misunderstanding 3: It reflects a deliberate desire to see others as similar; it is largely an automatic, unconscious process.
See Assumed similarity bias in everyday decisions
Pick a life context to see how this bias can show up outside the textbook.
Product Lead Overestimates Team Enthusiasm for Dark-Mode Toggle
A product lead assumes the team shares their excitement for a dark-mode feature, skips validation, and later finds low adoption.
Scenario
Jordan, a product lead at a midsize software firm, loved the idea of a dark-mode toggle and figured the team would feel the same. During a sprint planning meeting in the third-floor conference room, Jordan said, 'Everyone will appreciate this because I do,' and earmarked two sprints to build the toggle without checking with anyone. After the feature shipped, Jordan looked at the internal tool logs and saw that only five teammates had switched to night view, while the rest stayed with the default light mode. Customer-support tickets showed a few users confused by the unexpected option. Jordan realized the assumption had been anchored in personal preference rather than actual team or user taste.
Where The Bias Enters
Jordan used their own preference for dark mode as an anchor when estimating the team's and users' attitudes, failing to adjust sufficiently for differences in taste and needs.
Decision Check
Before committing the two sprints, Jordan could have run an anonymous poll or shared a low-fidelity prototype with a small group of teammates and users to gather real interest data.
This pilot example is illustrative and review-gated. It is designed to explain the pattern, not to claim a documented public case.
Sources
- Niroula, Rishab. REV 2.0 Topic Catalog. Hello to Halo.
- Kahneman, Daniel. Thinking, Fast and Slow. Farrar, Straus and Giroux, 2011.
- Gilovich, Thomas. How We Know What Isn't So. Free Press, 1991.
- Shermer, Michael. The Believing Brain. Times Books, 2011.
The next time this pattern surfaces, the move is not to fight it â it is to notice it. Naming Assumed similarity bias creates a moment of pause before the decision. That moment is usually enough.