The fundamental attribution error — overweighting disposition and underweighting situation — is not a random bias. It's how social cognition has to run given the information available to an observer.
When you watch someone act, the person is salient and the situation is background — you see them, not the pressures on them. From the inside, you feel the pressures; from the outside, you see only the actor. This asymmetry produces the actor-observer divergence, the self-serving bias, and most of what lay theories of personality get wrong about other people's behavior.




