In the description of an iterated prisoner's dilemma on Wikipedia, it states that in order for a game to be considered iterable, it must conform to the rule 2R > T + S, where R is the reward for cooperation, T is the temptation payoff, and S is the sucker's payoff. Could someone provide an example of a dilemma in which this would not be the case, i.e. it would be non-iterable?
The payoff depends entirely on how you set the game up. Here's one example of the case where $2R \leq T + S$:
Player B Cooperate | Defect Player Cooperate (1, 1) | (-2, 100) A Defect (100, -2) | (-1, -1)
Here, $R = 1$, $T = 100$, and $S = -1$, and $2R < T + S$.
Edit: To add a bit more value to the answer... any game could be played repeatedly (and thus is "iterable" in that sense.) However, my understanding is that the Wikipedia page writer means that for (Cooperate, Cooperate) to be sustained, you at least need this condition to be true.