<human>:  Who was the first psychologist to propose the theory of cognitive dissonance?
<bot>: That would be Leon Festinger. He proposed the theory of cognitive dissonance in the 1950s. Cognitive dissonance is the idea that people have a tendency to hold two conflicting beliefs at the same time. For example, if you believe that you are a good person, but you do something bad, then you will experience dissonance. This dissonance can cause you to feel uncomfortable, and you may try to reduce the dissonance by changing your beliefs.