Part: Part Five - Betting Before the Flop

Calling a shove

Pre-flop
Blinds 100 / 200Pot 2,700 (13.5 BB)BBA♣J♠● 25,000 (125 BB)YOUto actBTN● 2,400 (12 BB)Short buttonall-in 2,400 (12 BB)SBfoldsD

A short-stacked button open-jams 12 BB. The small blind folds and you're in the big blind with A♣J♠.

A 12 BB button open-shoves; you hold A♣J♠ in the BB, closing the action. Best?

WhyCall. A button open-jamming 12 BB has a wide range, and A-J is roughly a coin flip or better against it. You're getting better than 1.2-to-1 closing the action, so you only need ~46% - an easy call.
What happensYou call; he shows K-9 and your A-J holds.  You win the flip.
Against a wide short-stack shove you used pot odds and equity, not fear: getting a good price with a hand that's ahead of his range made it a routine call.

To call an all-in, weigh your equity against the price - wide shoving ranges make strong-but-not-premium hands clear calls when you're getting odds.