"Self-perception" refers to the way in which people come to understand their own attitudes and beliefs based on their behavior in given situations. It is effectively a model of oneself from the perspective of an outside observer.
For instance, according to self-perception theorist William James in 1884, outward behaviors such as frowning or sitting slumped in a chair come before the inward feeling they are supposed to represent. They inform the individual of their own emotions.
As such, one of the key implications of self-perception theory is that attitudes or emotions can be altered by changing behavior. That said, there is some variance in how strongly people are influenced by their own behaviors.