games
Iterated prisoner's dilemma
The same two players play the prisoner's dilemma again and again.
The same two players play many rounds, and each can see the earlier rounds. Cooperate means stay silent. Defect means confess. The score is points, and higher is better. Both cooperate: 3 each. Both defect: 1 each. You defect while they cooperate: you get 5 and they get 0. You cooperate while they defect: you get 0 and they get 5.
Play several rounds. Your partner can copy, forgive, or always defect.
In a single round, defecting scores more for you whatever the other person does.
When the same pair plays again, cooperation can last, because a later round can answer an earlier one.
Copying the last move starts by cooperating, then repeats what the other person just did, and returns to cooperation when they do.
Because you will meet again, both of you can end up cooperating. One round does not give you that reason.