In a 100 round game, one could precommit to play tit for tat no matter what (including cooperating on the 100th round if the opponent cooperated on the 99th). The opponent will do slightly better than oneself by cooperating 99 rounds and defecting on the 100th, but this is still better than if I had chosen to defect on the 100th round, as my opponent would have seen my precommit to be non-genuine and defected on the 99th round (and maybe even more). If I could have the paperclip maximizer use this strategy and I get to cooperate 99 times and defect once, that would be even better...but it won't happen. Oh well, I'll take 99 (C, C)s and 1 (C, D).