Definition
Similarity-attraction is a foundational finding in social psychology: people like — and comply with — others whom they perceive as similar to themselves. The similarity can be on almost any dimension: dress, opinions, age, ethnic background, hometown, hobbies, religious affiliation, even a shared first name. The effect is robust, fast, and largely unconscious.
In Cialdini's Influence, similarity is one of the five inputs to manufactured liking. It is also the strongest of the five for compliance work, which is why sales-training programs spend disproportionate time on it: mirror the prospect's dress, find common ground, identify shared experiences.
Why it matters
How it works
Two mechanisms drive the effect. First, similar others provide a kind of social validation — if they hold the same views or live the same way, our own choices feel less idiosyncratic and more justified. Second, similar others are easier to predict, and predictability lowers the cost of cooperation.
The compliance application is straightforward: an operator who matches the target's dress, mirrors a few opinions, and surfaces a shared connection becomes substantially more persuasive than an operator with identical credentials but no such matching. The matching does not produce belief in the operator's argument; it produces compliance with the operator's request.
The defense is to notice when the similarity feels too convenient. Striking coincidences ("I'm also from Cleveland!" "My daughter is also at Brown!") with sales contacts are often pre-researched. A genuine connection survives a small probe ("oh, what neighborhood?"); a staged one tends to deflect.