Pot commitment is the point where so much of your stack is in the pot, or the remaining bets are so small relative to it, that folding is wrong on price alone. The commitment decision is a plan you make on the flop, not a feeling on the river.
Before you act, ask: if all the chips go in, am I happy? At low SPR the answer has to be decided now, because one more bet or raise usually leaves you in a spot where folding is wrong on price alone. If the answer is yes, never put in a bet you would fold to a raise; choose between calling and raising by which line gets more chips from worse hands. If the answer is no, keep the pot small — check, or bet only if you are ready to fold to a raise and the bet still makes money.
The expensive line at low SPR is bet-fold: you put in a third of your stack and then give up the rest at a price you could not refuse. Short stacks and 3-bet pots make SPR low by default, so top pair with a good kicker and overpairs commit much more often there. At SPR 10 or more the opposite holds: one pair is rarely strong enough to stack off, and the hands that put in 100bb over three streets are mostly two pair, sets and better.
Worked example
FAQ
What does it mean to be pot committed?
It means the price of calling the rest of your stack is so good, relative to the pot, that folding a reasonable hand would be a mistake. At SPR about 2 or less, top pair with a good kicker or an overpair is usually committed.
How do you avoid committing with the wrong hands?
Decide on the flop. If a hand cannot call a shove, do not bet a third of your stack with it: check and keep the pot small instead.