According to psychologist Timothy Wilson:
People draw inferences about who they are by observing their own behavior.
Self-perception theory turns common wisdom on its head. Two powerful ideas follow from it. The first is that we are strangers to ourselves. After all, if we knew our own minds, why would we need to guess what our preferences are from our behavior? If our minds were an open book, we would know exactly how honest we are and how much we like lattes. Instead, we often need to look to our behavior to figure out who we are. Self-perception theory thus anticipated the revolution in psychology in the study of human consciousness, a revolution that revealed the limits of introspection.
But it turns out that we don’t just use our behavior to reveal our dispositions—we infer dispositions that weren’t there before. Often, our behavior is shaped by subtle pressures around us, but we fail to recognize those pressures. As a result, we mistakenly believe that our behavior emanated from some inner disposition.