TRY TO MAXIMIZE YOUR CHANCES
Mark Twain claimed: "Necessity is the mother of taking chances."
We have chances in bridge: for example, the chance that the contract will make. With finesses, what are the chances that one, or one out of two, or one out of three will work?
In today's deal South has finesses available in all three side suits. However, because he is in a small slam, he cannot afford to take two that lose. How should he play in six hearts after West leads a trump, and East follows suit?
The bidding followed a modern path. Two no-trump was the Jacoby Forcing Raise, guaranteeing game-going values with at least four-card heart support. Four no-trump was Roman Key Card Blackwood. North's reply showed the trump queen and two key cards (two aces, or one ace and the trump king). Five no-trump announced that all six key cards (four aces, the trump king and trump queen) were held and that South was thinking about a grand slam. Six hearts denied a side-suit king.
Declarer drew trumps ending on the board, then played a diamond to his queen. Sadly, it lost, and a diamond came back. Now South needed to maximize his chances in the black suits. He won with his diamond ace, cashed the club king, played a club to the ace, discarded his last club on the diamond jack and ruffed a club. Here, the queen appeared to establish dummy's jack, so the contract was home. But if the queen had not been seen, declarer would have crossed to dummy with a trump and tried the spade finesse.
The percentages on those finesses are basically 50, 75 and 87.5.