That's not unreasonable, but I think that a lot of the problems people have come from not even really trying to be careful.

I think selection effects explain almost all of this phenomenon. My nerdy friends don't really have trouble holding to their pre-commitments. The reckless 20 year olds I meet in bars don't even really understand the idea of pre-commitments, and the whole thing is just sort of...uncool, to them.

People don't regularly pre-commit to how much TV they'll watch, how much internet they'll surf, or how much chocolate they'll eat --- and when they do, I expect they fail often. When it comes to alcohol, two drinks becoming many is a total cliche.