After West cashes two rounds of spades and forces South to ruff a third, a not-so-alert declarer (not you, of course) might simply draw two or three rounds of trumps and only then comprehend the problem with this hand: Plan A will not work! Plan A was to draw three rounds of trumps and discard South's losers on the solid diamonds. West has enough trumps to spoil that plan; and worse, once you ruff the spade, he now holds as many as you do. If you let him in again, he will continue the spades and cause you to lose control of the hand.

This line of defense is called "tapping" the declarer: repeatedly leading the top cards of a non-trump suit to force declarer to have fewer trumps than the defense has. To foil this defense, one must figure out how to turn off the "tap".

After you lead a small heart to dummy's K and a small heart from dummy, East shows out and you get the picture. Click to see the pic. What you must do at this point, is implement Plan B: duck the trick into West.

Yes, he still has as many trumps as you do; but it no longer does West any good to continue the spades since dummy rather than declarer can ruff. Put another way, you have taken the pressure of the spade ruffs off the hand that can ill afford it, and have given this task to the hand that can afford it.

This approach, by the way, shows one way in which intermediate players become advanced. Beginners learn techniques on how to win tricks (finesses, ruffs, etc.); advanced players learn how to effectively lose tricks (holdups, throw-ins, ducking, etc.).