Biography
It's never easy to admit that we are responsible for our actions and deserve to be blamed — in fact, for some people it's one of, if not the most difficult thing(s) to do — and it is often far more comfortable to play the Blame Game and convince ourselves that it is the fault of another, even though this is the coward's way out. We may blame others even when we know deep down in our hearts that it is our fault. Due to the Rule of Drama, fictional characters will blame themselves for things going south most of the time, but there are some cases where the character who really is to blame will blame everyone else instead. Common variations include:
The person stuck with the blame fails to defend himself, perhaps out of sheer dumbfoundedness at the other person's gall.
The blame-shifter offers an absurdly flimsy pretext for ducking responsibility.
The character does this all the time... and consistently gets away with it.
The person can't comprehend what they did is wrong because of how innocently they did it.
The person genuinely believes that they acted in an acceptable manner in response to another's unacceptable provocation, and genuinely believes that others are wrong for feeling angry with them.
The person thinks they're the last sane person in a world of unreasonable idiots; therefore, anyone who blames them is wrong.
The person thinks they're morally correct or righteous, and thus it is impossible for them to be at fault because they did the right thing, even when it wasn't.
The person never outright denies responsibility, but instead dodges the issue entirely, usually via a bunch of platitudes about becoming a better person without ever actually taking direct responsibility for their behavior.
Sub-Trope of Psychological Projection. This is a frequent component of Comedic Sociopathy and Revenge Myopia. The diametric opposite of It's All My Fault or At Least I Admit It. A character prone to this will likely try Glad I Thought of It, too. Compare Hypocritical Humor, which can involve a similar blindness to one's own flaws, and Implausible Deniability. See also It's All About Me and Narcissist, which are key reasons why a character would fall into any of the above. Also compare Backhanded Apology, an insult disguised as an "apology" where the perpetrator attempts to shift blame onto their victim e.g. I am sorry you were so stupid as to fall for my deception. If the character doesn't blame others, but isn't sorry for what s/he's done, see The Unapologetic (however, the two tropes can overlap, generally when the character says "I Did What I Had to Do"). This trope is the defining characteristic of The Unfair Sex. Can overlap with Everything Is Racist, when the person blames their failings which are clearly their own fault on societal prejudice and hatred towards people of their race/gender/sexual orientation/taste in music/whatever. If the person is upset that their victims dared to fight back, s/he is likely Feeling Oppressed by Their Existence. A rebuttal to this trope would involve Stopping the Blame Game.
The formal term for this is "self-serving bias", and it is a key personality trait of both The Sociopath and the Narcissist. Related cognitive biases include the defensive attribution hypothesis, as well as the fundamental andultimate attribution errors. Even in the average person, the brain is designed more for self-defensiveness and maintaining its own comfort than for strict accuracy, explaining why it can be so difficult for people to accept they made a mistake or change their opinions even in the face of clear evidence.
Compare with Mama Didn't Raise No Criminal, for parents that try to shift blame off of their kids, rather than themselves. Subtrope of the Sin of Pride.
NOTE: Please remember that examples of people blaming others for something that's clearly the fault of someone else (i.e. a third party) is not an example of this trope; that's Misplaced Retribution. This trope is only for when people attempt to shift the blame off of themselves.