Suppose you like someone very much. Then, by a familiar halo effect, you will also be prone to believe many good things about that person - you will be biased in their favor. Most of us like ourselves very much, and that suffices to explain self-assessments that are biased in a particular direction.

Nobody would say, 'I'm voting for this guy because he's got the stronger chin,' but that, in fact, is partly what happens.

We are very influenced by completely automatic things that we have no control over, and we don't know we're doing it.

Daniel Kahneman Quotes