This came up yesterday in a practice session with Kathy on BridgeBaron. You’re in a very dicey 3NT contract where you opened 1NT and your vulnerable LHO overcalled 2H (DONT, but it doesn’t really matter). You need to get 3 tricks from the Diamond suit with this layout:
Dummy: Q852
You: K976
What’s the best way to play this suit? Your only chance for 3 tricks is if one of the players has a doubleton ace. If you had X-ray glasses you’d see which opponent has this. Lacking X-ray glasses or the hand record for the session, we’re going to presume LHO (the bidder) has it, so our presumed suit layout is this:
Q852
AJ, A10, or Ax J10x, Jxx, or 10xx
K976
If you knew the cards were placed this way then the winning play is low to the Q and then duck a diamond to the now bare Ace. When you’re playing the hand you don’t know for certain, but given the information available, this is the best chance to get your 3 tricks.