Discovered by Leon Festinger in 1957.
In the famous "\$1 vs \$20" experiment, participants were asked to lie that a boring task was interesting.
Group paid \$1: "Actually, it was kind of fun."
Group paid \$20: "I lied for the money."
Surprisingly, the \$1 group actually remembered the task as more enjoyable. They couldn't justify lying for a small reward, so they changed their attitude to match their behavior.
Our brains hate contradiction. So instead of changing our actions, we often change our thoughts to maintain consistency.
Social
Cognitive Dissonance
The psychology of why we justify bad habits