Consider an argument between two closely bound people, say, husband and wife. Both parties believe that one is an altruist—of long standing, relatively pure in motive, and much abused—while the other is characterized by a pattern of selfishness spread over hundreds of incidents. They only disagree over who is altruistic and who selfish. It is noteworthy that the argument may appear to burst forth spontaneously, with little or no preview, yet as it rolls along, two whole landscapes of information processing appear to lie already organized, waiting only for the lightning of anger to show themselves.
That is by Robert Trivers in his book Social Evolution. I haven't read it, I found the quote from Steven Pinker's How The Mind Works
