tit-for-tat

“Here's the weakness of tit-for-tat. Sometimes people make mistakes. And not because they're mean, or, I mean, just, Mistakes happen. Sometimes you are trying to be nice, and a person interprets it as an insult. Now, if that person is following a tit-for-tat mo…”

“In fact, it was the shortest computer program submitted, only four lines of code. On the first move, cooperate, and on every subsequent move, do whatever the opponent did on the previous move.”