Ruffing Winners, no losers, this sort of situation occurs every now and then…
West opens the King of Clubs against Four Spades. Declarer wins with dummy’s Ace and leads a Heart. That is his normal line of play. Since one of dummy’s two entries is knocked out at the first trick, he takes the opportunity to finesse the Hearts. Doubtless, he hopes to use dummy’s second entry for another finesse later, and to draw trumps in between. But what about East? Work out what will happen : (a) if he ruffs, and (b) if he does not.
Take (a) first. Declarer will part cheerfully with the deuce of Hearts, ruff the Club return and draw trumps in two rounds. Now he will cash the Ace of Hearts and lay down the Queen. West will glare furiously at East, and East will wear a look of injured innocence. For this will be the unhappy picture.
The defence is powerless. West can take his Heart King, but the Knave is trapped. And it all happened because East ruffed so injudiciously.
The time has come to try (b). East discards a Diamond or a Club and sits back. Declarer is helpless. If he draws trumps, he will lose three Hearts. And if he does not, East will over-ruff a Heart—after West has gathered two tricks with his King Knave.
What exactly would a post-mortem reveal? Why was that ruff so fatal? Because, the coroner would say, East used a precious trump to ruff the deuce of Hearts. That is all he achieved. Later, at the Old Bailey, East might plead that » he did not know his trump was loaded «. He thought that it was of little use, anyway. That proved a serious error, but how was he to know?
The judge would rule that even a seemingly useless trump should not be wasted on a miserable deuce that was a loser from the start. And that is the kernel of the matter.
In other words, ruff CONSTRUCTIVELY—to deprive declarer of a winner, to promote a trump in partner’s hand, to take the lead when you want to be on play. But do not ruff just because you think that your trump is not much good anyway.