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 the ♣T and you hold up your Ace. East continues the suit, and it looks safe to win that one (surely West is now out of Clubs). Can you make nine tricks if East holds the ♦A? No, if East has that card then the contract will be down on the run of the Clubs. So, to make 3NT, you must assume that West has the ♦A. Next question. Where is the ♦Q?