A self-serving bias is any cognitive or perceptual process that is distorted by the need to maintain and enhance self-esteem, or the tendency to perceive oneself in an overly favorable manner.
Remember that time you bought something totally unnecessary, faulty,
or overly expense, and then you rationalized the purchase to such an
extent that you convinced yourself it was a great idea all along? Yeah,
that's post-purchase rationalization in action — a kind of built-in
mechanism that makes us feel better after we make crappy decisions,
especially at the cash register. Also known as Buyer's Stockholm
Syndrome, it's a way of subconsciously justifying our purchases —
especially expensive ones. Social psychologists say it stems from the
principle of commitment, our psychological desire to stay consistent and
avoid a state of cognitive dissonance.