Long overdue post on the gap concept:

So you've put the villain on a (goddamn) range, what next?

Picture the villain's range as a line:

Code:
Bottom                      Average                       Top
   |---------------------------|---------------------------|
At one end, we have the bottom of the villain's range. At the other, the top. Roughly speaking, if we want 50% equity or better against a villain's range our hand needs to be 'above average', so our calling range is half of the villain's perceived range. If they are shoving 50%, we call 25%. Simples.

If we are applying our ranges correctly, the actual hand they show up with is irrelevant. If we call with KK against a wide shoving range and they have AA this time, good for them. If you made that call 100 times you'd win far, far more than you lose. Always play a range, not a hand.

Now there are many, many situations where we are happy to call with less than 50% equity, thanks to our friends Mr Pot Odds and Miss Implied Odds, but more on those later (maybe). What I actually want to discuss is how the gap concept applies in tournaments.

Firstly, there is chip utility. Your ability to survive and win depends on you having a stack in front of you. No chips, no win. When a villain shoves into you and you are likely a 50/50 flip vs their range, are you willing to risk your tournament life on a coinflip?
Do they have your stack covered, or could you call and still be left with a playable stack if you lose?
are you ITM or on the bubble?
can you afford to wait for a better spot, or has the time come to double up or go home?
I'm still developing in this area.

Second, fold equity. You generally have approximately 1.2fucktons of FE when you raise or reraise in tournaments (ymmv), you have zero FE when you call. There is no chance of winning without showdown when deciding to call a shove or not, your only hope is to have the best hand by the river. Winning without showdown is huge, because it leaves nothing to chance.

I don't know if I explained myself very well, but basically if you're calling a raise (especially a shove), you need a much, much stronger hand than one you'd happily open yourself.

Comments & corrections welcome.