Ok goddammit, I'm drunk, but I'll tell ya what.
Lift with what you can fail with in 6-12 reps. But you don't HAVE to fail in that range. You can also do more sets and get the same effect. Failure is caused by like 10 different biological reasons. There is no magical growth signal. The growth is caused by the degradation of protein in relation to energy expended. Working in the given growth range, that will result in hypertrophy. So do it.
Pretty decent advice for a drunk guy...
umm....i'll drink to that. that was a pretty cohesive statement.:alcoholic