Deal 16
 
  3NT
♠ 7 5 4 2
K Q
A 5
♣ K J 10 8 5
 
 WEST  NORTH  EAST  SOUTH
1♣1♠2NT
pass3NTpasspass
pass

The bidding has been as shown.
Partner led the ♠Q, a low card was played from dummy, and it is your play.

When you have made your choice click NEXT .
♠ Q


♠ K 10 9 8 6
8 7 4
Q 7 4
♣ A Q
 


 

 
Deal 16
 
  3NT
♠ 7 5 4 2
K Q
A 5
♣ K J 10 8 5
  Play the ♠K.

It seems that perhaps you should play low and let partner's ♠Q force out South's ♠A. Then, when you get the lead with a high ♣ you can force out South's ♠J. Get the lead with your other high ♣ and set the contract with ♠s.

Suppose you try that. Play low on the first ♠.
South will also play low and West will be left holding the trick, and also holding the bag!
With no more ♠s West will have to play one of the other three suits, and that is just what South wants to have happen. The contract could no longer be beaten.

Now do it the right way.
Play your ♠K on partner's ♠Q. Assume South takes the trick, although it doesn't matter whether he wins the first one or holds up.
When you win your first ♣ drive out South's ♠J.
When you win your second ♣ trick your ♠s will be good.
If you overtake the first trick the contract can no longer be made.

Notice that South will always make two ♠ tricks, so your overtake costs nothing.

 Deal 17 
♠ Q
10 9 6 5 2
J 8 6 3
♣ 6 4 2
♠ K 10 9 8 6
8 7 4
Q 7 4
♣ A Q
  ♠ A J 3
A J 3
K 10 9 2
♣ 9 7 3