Humor keeps ego from becoming the only narrator.

Your ego is a narrator with a strong preference for one interpretation, the one where you were reasonable and the situation was unfair. Humor introduces a second voice, one that can see the same scene and find your position slightly absurd. Having both available keeps you from being fully captured by the flattering version.

After a moment where you felt very certain and very wronged, try telling the story as a comedy in which you are the ridiculous one. You do not have to believe that version entirely. You only need it available, because a person who can laugh at their own account of things is much harder to trap inside it.