I agree with Fonzi that JJ is a lot about feel, say your in late position and you got someone raising 4xBB UTG and 2 caller ahead, you have to go on your reads so far of the players in the hand, are they holding each others outs? (e.g. AK, AQ, KQ) which puts your hand in an advantageous position.
Or are you in trouble with a higher pair and over cards out there, which leave you drawing to 2 outs.
Having made the call say, we then have at least one of the other players making a C-bet before you and you need to use the flop and your hand ranges of your opponents to decide if they're just making a continuation bet or whether they're trying to get more value out of a hand they're winning

this is probably why most inexperienced players in tourny's just throw it all in preflop hoping to get a lucky break and double up or better, the more experienced player juggles the odds and his instincts to minimise loss while maximise profit, they may not treble up, but they don't run as much risk of donking out either