...yeah, it's not a brilliant rationality quote, but there's a bit of a good point in it nonetheless: this is a case in which precommitment is necessary, because despite the fact that you would prefer not to be subject to the assault of an enemy, you don't want to establish that every threat will be profitable, however imaginary. Naive calculations neglect the effect of your decision method on the actions of others. (It's like in cryptography - your strategy has to work even if other people know the function.)