This deal was played in the top knockout bracket of the 2016 Gatlinburg regional. Both expert declarers went wrong. See if you can do better. South held: 

 A109  
 AJ5  
 1065  
 AK106.

Vulnerable against not, 2 passes are followed by a 1 opening on your right. You overcall 1NT and partner uses 2 (Stayman). You answer 2 and partner bids 3NT. The 6 is led and you see:

QJ83  32  KQ92  Q92

A109  AJ5  1065  AK106

Declarer has only 5 top tricks. If the KQ of hearts are with RHO, that means 6 tricks. A spade finesse could produce at least 2 more. Clubs could produce an extra trick and the diamonds also are a source of tricks. The stopper situation is shaky. Do you have two heart stoppers? What is your plan?

East plays the Q and both expert declarers won the A. Next they played a diamond to the king and ace. Back came a low heart. If you think the opening leader has something like Kxx, you can block the suit by playing low. LHO would have to win the third round with the king and RHO would have no entry. On the other hand, if you play low on round 2 of hearts and RHO actually started with the KQ, you will never get your J. Both declarers guessed to play the jack (reasonably playing the opening bidder for KQxxx). The jack won the trick. Now what? Let's look at the Real Deal:

Vul:N-S Dlr: West	QJ83  32  KQ92  Q92
K764  1076  J874  87		52  KQ984  A3  J543
	A109  AJ5  1065  AK106

The 6 lead went to the queen and ace. A diamond to the king lost to the ace and a low heart was won by declarer's jack. We can see that declarer can make the contract by guessing well in both minors (finessing against both jacks). That would give him 4 clubs, 2 diamonds, 2 hearts and the A. Without the benefit of seeing all 4 hands, both declarers naturally relied on the simple spade finesse (through the opening bidder). They crossed to the Q and led the Q. If the finesse had won, they'd have had at least 3 spades, 2 hearts, 1 diamond and 3 clubs for the contract. When it lost, West returned a heart; down 1.

Where did declarer go wrong? Not by taking the reasonable spade finesse, but at trick one. If he was going to always play RHO for the KQ, it is best to duck the first trick. Why does that matter? East plays a heart at trick 2, won by the jack. Now a diamond goes to the king and ace. East clears hearts, but West has no hearts left. When declarer goes to dummy for the spade finesse, West takes the king, but has no hearts left. Declarer easily makes the contract. This was just your basic holdup play.