Intermediate and newcomer players - sharpen your game with this series of tutorials. You can browse the index by topic, or read them in order. Learn even more at ACBL's Learn page.
West leads his 4th best Diamond and, as this is the Three, and considering the bidding, it is clear that West had led from a five-card suit. East wins her Ace, and you ruff the Diamond continuation. Before drawing trumps, you might as well play the ♣K, hoping to force an entry to Dummy. But E-W are up to the challenge and the King is allowed to hold the trick. How did E-W know that you were not trying to sneak through the singleton ♣K?