The answer is: Self-serving bias
Self-serving bias is a psychological defense mechanism that people automatically adopt when we are trying to maintain our self-esteem. The effort to maintain this self esteem is why we tend to minimize personal responsibility if we do poorly.
For example, let's say that Bill fail his math class. Rather than acknowledging that bill did not put enough effort in the study, he would tell himself that the math class would no give any benefit to him.
