See if you can work this one out:
You, South are in 3NT, with East having bid spades, West dutifully leading one. How do you plan the play?
Six top tricks are readily available. For more you must look to the clubs. That involves the risk of letting in East, the dangerous opponent, but this risk must be taken. The SA is held up till the third round and the CQ finessed with trepidation and then relief as it wins. What next?
There is an instinctive tendency to play the CA and then a small club. If West wins the third club trick with the CK, all is well. He has no more spades or the suit breaks 4-4 which is almost as good. But West may have started with CKx only. Then he will drop his king on the ace and control of the suit will pass to East's jack.
The declarer, who thinks ahead and works it out, will make her contract. The others will be "unlucky".
Having brought off the club finesse, the thoughtful declarer returns to her hand with a heart or a diamond and plays towards the CA. If West's king goes up, she ducks, playing a small card from dummy, not the ace. East, the dangerous opponent, is powerless. He cannot overtake partner's king and has no possible entry outside clubs. As long as clubs break 3-2 declarer is home.
Making the contract depends on two things. Firstly, holding up the SA, so as to make it safe to lose the lead to West, the now harmless opponent. And secondly, visualising the distribution of the five outstanding clubs. To succeed, West must have the king. That is luck. The rest is card play technique.
This hand and most of the text is taken from pages 85-6 of Card Play Technique (or the Art of Being Lucky) by Victor Mollo and Nico Gardener (revised edition, 2013). This is a much loved classic and would benefit any interested bridge player. There are copies in our club library.