You open 1NT and after a Stayman inquiry end up in 3NT with the ♥2 lead. (fourth best leads).
Dummy: ♠QJ64 ♥KQ94 ♦J432 ♣Q.
Your hand: ♠A75 ♥63 ♦AQ96 ♣AJ73.
You put in a high heart. RHO takes the ♥A, thinks a bit and returns the ♣2. LHO takes the ♣K; thinks a bit and returns the ♣4. RHO plays the ♣10 and you take the ♣J.
At this point, you expect one heart trick (unless they set up Dummy's ♥9 for you); two clubs; two spades (by force) and two diamonds by force. However, you can only afford to lose two more tricks.
The diamond suit gives you a CHOICE of plays. You can play for King doubleton in RHO's hand; get to dummy, play diamond to ♦Q, cash the ♦A, hope the ♦King falls and return to ♦J on dummy. OR, you can play for ♦K10x of diamonds in RHO's hand. In that case, you need to lead ♦J from Dummy; when it is (presumably) covered by the ♦K, you play ♦A; return to dummy and finesse the ♦10 next time. [Note that you only have a choice because you own the ♦9—without that card, your only choice for four diamond tricks is ♦Kx onside.]
Dummy doesn't have many entries. However, your best chance for THREE spade tricks is to find the ♠K on your left. Also, considering the distribution, you know that LHO started with exactly four hearts (led the two). You know that clubs are 4-4-4-1 around the table (because RHO shifted to the ♣2 and LHO returned the 4—lowest outstanding—after winning the ♣K).
Therefore, LHO's most likely shape is 3-4-2-4 OR 2-4-3-4. If the first distribution is the case, the second choice of diamond plays is favored. So, trick three, put a LOW spade on the table. (You want LHO to take the ♠K right away if s/he has it and if LHO does have a doubleton ♠K, will be hard to duck.) If LHO does duck, play the ♠Q (which wins). Play the ♦J, which fetches the ♦K, and kill the King. Then play the ♠A and a low spade. Now LHO must decide whether to play a heart or a club. If he plays a club, take your Ace.
Go over to the high heart and cash the good spade, discarding a club.
LHO is highly likely to keep both remaining hearts and the good club and discard a diamond. If you trust your count on the hand, finesse to your ♦10. You'll end up losing one spade, one heart and one club, making four.