A character who, due to previous experiences, should know better, but doesn't. But later, they display that they do. But then they don't, and so on, and so forth.
This is extensively used either for quick, cheap momentary jokes and gags, or to hold the plot of the particular episode together. It also helps maintain the status quo. Expect to find it in a series with inconsistent character development and Negative Continuity. Sort of the milder, Zig-Zagged Trope sister of the Idiot Ball.
Compare Idiot Ball, Smart Ball, and Aesop Amnesia. See also Depending on the Writer. Usually justified by Rule of Funny.
