Part: Part Five - Betting Before the Flop

A small pair, short-stacked

Pre-flop
Blinds 100 / 200Pot 900 (4.5 BB)CO6♠6♦● 3,000 (15 BB)YOU15 BB stackUTG● 9,000 (45 BB)Openerraises 500 (2.5 BB)SB● 9,000 (45 BB)posts 100 (0.5 BB)BB● 9,000 (45 BB)posts 200 (1 BB)BTN● 9,000 (45 BB)BTND

You have a 15 BB stack. A player opens to 500 from under the gun and it folds to you on the cutoff with 6♠6♦.

15 BB deep, an opener makes it 500 (2.5 BB); you hold 6♠6♦ on the cutoff. Best?

WhyWith only 15 BB behind you can't set-mine - call 500 and even when you flop a set there aren't enough chips left to win to justify it. Jamming instead collects the dead money and blinds through fold equity, and sixes are rarely in dire shape when called. That's the short-stack way to play a small pair.
What happensYou shove and this time he calls with A-K; a king pairs and you're out of the flip. The jam was still correct - short-stacked you were taking fold equity plus a live coin flip, and a +EV shove doesn't stop being right because the flip lost.
The pocket sixes you'd set-mine 150 BB deep are a 15 BB jam - and even when the jam is called and loses the flip, taking your equity and fold equity now was right. Stack depth rewrites the plan for the same two cards.

Set-mining lives on implied odds, which need deep stacks - short-stacked, a small pair becomes a shove-or-fold hand that banks equity plus fold equity now, not a speculative call-and-pray.