It gets presented as an obvious and basic game theory result, but it only makes sense if you don't believe in the basic tenants of game theory, amongst which is the claim that it is a theory of maximizing rational actors.
There is no moral choice-making for maximizing rational actors, and both actors in the PD have exactly the same information, including the fact that the other individual is a maximizing rational actor. As such the off diagonal elements of the payoff matrix are irrelevant to any rational decision making because any two rational actors with the same goal will always make the same choice in the same situation. To do anything else would be irrational.
So within the frame of the theory both players know with certainty that because the game is being played by maximizing rational actors that the other player will always do exactly what they do. This is true no matter what they do: the other player will always reach the same conclusion. Rationality dictates it, if rationality means anything at all.
It is only when you smuggle in the possibility of an irrational choice on the part of one of the players that the off-diagonal elements become relevant, because one player can for unaccountable reasons choose to do something irrational, which a maximizing rational actor would never do.
Game theory is not about people. It's about rational actors who want to maximize their payoff. For such entities there is no dilemma, since only the diagonal elements of the matrix matter, and cooperation is the obvious maximizing strategy.
Unfortunately, game theory under this constraint becomes very boring. There is probably a salvagable variant of it that remains interesting, but I'm honestly not sure what it's a theory of. "Semi-rational not-very-smart actors"? That would describe humans reasonably well, I guess. It certainly describes me. Or maybe the decision-maker being analyzed could be considered a rational actor and the rest of the players irrational, although that would be equivalent to playing against a random number generator.
There is no moral choice-making for maximizing rational actors, and both actors in the PD have exactly the same information, including the fact that the other individual is a maximizing rational actor. As such the off diagonal elements of the payoff matrix are irrelevant to any rational decision making because any two rational actors with the same goal will always make the same choice in the same situation. To do anything else would be irrational.
So within the frame of the theory both players know with certainty that because the game is being played by maximizing rational actors that the other player will always do exactly what they do. This is true no matter what they do: the other player will always reach the same conclusion. Rationality dictates it, if rationality means anything at all.
It is only when you smuggle in the possibility of an irrational choice on the part of one of the players that the off-diagonal elements become relevant, because one player can for unaccountable reasons choose to do something irrational, which a maximizing rational actor would never do.
Game theory is not about people. It's about rational actors who want to maximize their payoff. For such entities there is no dilemma, since only the diagonal elements of the matrix matter, and cooperation is the obvious maximizing strategy.
Unfortunately, game theory under this constraint becomes very boring. There is probably a salvagable variant of it that remains interesting, but I'm honestly not sure what it's a theory of. "Semi-rational not-very-smart actors"? That would describe humans reasonably well, I guess. It certainly describes me. Or maybe the decision-maker being analyzed could be considered a rational actor and the rest of the players irrational, although that would be equivalent to playing against a random number generator.