Part: Part Nine - Inflection Points: M, Q & the Zones

The re-shove

Pre-flop
Blinds 400 / 800 (100 ante)Pot 3,900 (4.9 BB)Your M = 5 • Red zoneBTNA♠10♠● 10,500 (13.1 BB)YOUto actCO● 18,000 (22.5 BB)Openerraises 1,800 (2.2 BB)SB● 18,000 (22.5 BB)posts 400 (0.5 BB)BB● 18,000 (22.5 BB)posts 800 (1 BB)D

Red zone (M ~5). A player opens to 1,800 from the cutoff and it folds to you on the button with A♠T♠.

Short (M ~5), a cutoff opens, you hold A♠T♠ on the button. Best?

WhyCall and you've committed most of your stack to see a flop you have no chips to navigate - the worst of both worlds. Jamming over the cutoff's open puts the decision back on him, A-T suited is plenty strong to be called and race, and the open even left extra dead money worth attacking. Re-shove or fold, never flat.
What happensHe calls with pocket jacks and your ace never arrives - you bust. Sting aside, the re-jam was correct: A-T suited wins outright often enough, and races well enough when called, that shoving beats folding. A cooler doesn't make the decision wrong.
When you're short and someone opens, three-bet all-in instead of flatting - you gain fold equity you'd otherwise have none of, and you're never in terrible shape when called. The play is right whether or not this particular flip falls your way.

Short and facing a raise, the flat is a trap - you can't play a flop with five big blinds. The re-shove buys fold equity on top of your equity: jam over the open or let it go.