Why does making a decision tend to generate dissonance, how is this dissonance reduced, and under what conditions is postdecisional dissonance reduction the greatest?

Why does making a decision tend to generate dissonance?

When a person has a decision to make, that is has to choose between choices, the person will have a negative cognitive conflict (dissonance).

How is this dissonance reduced? Ways to reduce dissonance is to basically have more options to choose from. Another way is to reduce the importance of the situation through attitude and/or belief.

Under what conditions is postdecisional dissonance reduction the greatest? This can be achieved when a person convinces themselves that the choice they made cannot be changed