Positivity effect
（重定向自Positivity bias）
In psychology and cognitive science, the positivity effect is a term given to three different phenomena. It is the ability to constructively analyze a situation where the desired results are not achieved; but still obtain positive feedback which assists our future progression. When considering people we like (including ourselves), we tend to make situational attributions about their negative behaviors and dis-positional attributions about their positive behaviors. We probably do the reverse for people we do not like.
This may well be because of the dissonance between liking a person and seeing them behave negatively.
example: If my friend hits someone, I will tell him that the other guy deserved it or that he had to defend himself.