Wouldn't this be a problem for tit for tat players going up against other tit for tat players (but not knowing the strategy of their opponent)?
Only if it's common knowledge that both players are human.
ETA: Since I got downvoted, maybe I wasn't being clear. I think that the Warren Buffett quote applies to human psychology more than to game theory in general. If outright deception were easy, it would probably become a good strategy to keep your allies in some doubt about your intentions, as a bargaining chip. But we humans don't seem to be good at pulling that off, and so ambivalence is a strong signal of opposition.
A monthly thread for posting rationality-related quotes you've seen recently (or had stored in your quotesfile for ages).