We are predisposed to see other people as having enduring characteristics that cause them to behave in predictable ways, and to interpret samples of behavior—even hopelessly inadequate samples—as clues to their characteristics. Our theory of human nature leads us to expect that people will be consistent…
The predisposition to attribute someone’s behavior to something within them that’s relatively stable and enduring—something that nowadays is called personality and that used to be called character—actually causes us to make errors in prediction; we expect people to be more consistent than they really are.
—Harris, J. R. (2006). No two alike: Human nature and human individuality. New York: W.W. Norton & Co.
Definition of fundamental attribution error from Judith Rich Harris.