Checklist to make sure the Greek gift sacrifice will work in a certain position:
- The opponent has castled kingside.
- You must have a bishop that can sacrifice itself for the h7/h2 pawn.
- The pawn must not be defended by any piece other than the king.
- You must have a knight that can hop into the g5/g4 square that can give a check in case the king takes the bishop.
- The g5/g4 square must be protected. Otherwise the knight can just be taken by the opponent's queen.
- You must have a queen that can land itself in h5/h4 to threaten checkmate. The only way to prevent checkmate is for the opponent is to give up the queen for the knight, or to protect the h7/h2 square.
- The opponent must not have a way to protect the h7/h2 square directly with a bishop on the h7-b1/h2-b8 diagonal. This is the condition that is forgotten the most.
An example of a position where the greek gift sacrifice is possible: