Let's say you're in four hearts and West leads a club. You win with the ace and play the A-K of trumps, hoping for a 2-2 split. When East turns up with three trumps, you shift your attention to spades by playing the A-J and another spade. Unfortunately, East ruffs the third spade and returns the queen of diamonds, and down you go.

You could certainly claim to have been very unlucky, since you would have made the contract had the trumps divided 2-2, or if West had the three trumps, or if East had the ace of diamonds, or if East had three or more spades.

Even so, the fact remains that the contract can be made with more careful play. After East follows low on the first trump lead from dummy, the correct line of play -- by far -- is to finesse the ten! In the actual deal, the ten wins and you finish with 11 tricks. But that in itself doesn't prove that the ten is the right play.

Finessing the ten is best because it has the great virtue of practically guaranteeing the contract, and not because you luckily find East with the Q-J-x. Indeed, you don't really mind losing a trump trick to West, because you're certain to score at least 10 tricks -- five hearts, four spades and a club -- if you do.

The primary concern is that East might have three trumps and later gain the lead to return a diamond through your king. The first-round trump finesse guards against this possibility. It is true that the deep finesse will sometimes cost a trick unnecessarily, but that is a tiny premium to pay for ensuring the contract.