It's only the best answer if the other party is bothering to seek the best answer in real time, and in ways that you can't predict. If your opponent is governed by some algorithm, which is the case for torrent clients, you may need to depart from tit for tat in order to break them out of a needlessly adversarial mode. Or, if you're feeling like the bad guy today, you might need to depart from tit for tat to put them in an irrationally cooperative mode.