LEARNING CENTER

West is the dangerous hand. You don't want to lose a trick to West, but if West has the A, then you are just going to go down. This is a hand where you only need to hold up once to break communications (East likely only started with 2 spades), but it's better to hold up twice and force East to pitch something (and also sometimes reveal that West preempted a five-card suit). Play diamonds as soon as you win the A. If you go around guessing other suits, you may go down an extra trick. If West has theA, then you'll go down two and others may go down three. 

West. The concern is that if West leads a diamond, you might lose three diamond tricks. Since if East leads diamonds, your king will be a winner, you should only risk losing to that side. There is a nursery rhyme on when to finesse for a queen: eight ever nine never. As with fairy tales, there is some truth (finesse with 8), but nine never is just a suggestion (and only right a little more than half the time). Here, the other considerations should lead you to play the K and then finesse, planning on throwing away diamonds later on your clubs. 

East. Be very careful when the opponents choose to lead a suit you've shown. This lead looks to be a singleton. Win trick one with the A and play a trump. Which way should you finesse hearts? It's a trick question, you shouldn't guess trumps and go down when you can afford to lose a trick in each of clubs, diamonds and hearts. Lay down the AK.

East. If East gets in, he can play a high heart through your holding. To protect against this, at trick two play a club to dummy and play a diamond to the 10. If West wins, nothing bad can happen. If you started playing all the high diamonds first, and East started with Jxxx of diamonds, you will go down unless clubs split 3-3. At matchpoints, the decision is closer. Normally you'd play for a 3-2 split, but the preempt changes the odds. 

West. If West is on lead, he can play a club through your king. East is safe on lead. Duck the first trick. Now if East returns a diamond, you can take your heart finesse and even if it loses, East can't attack clubs. You will eventually throw dummy's clubs away on the spades.

Both. Win this trick. If you duck it, then a good opponent (who watches a signal from partner) may switch to a heart, ending your chances of making your contract. You get half-credit if you said West since it is, in fact, dangerous if you choose to lose trick one to West. You need to knock out the A before opponents play hearts.