This deal comes from the Round of 64 of the 2009 Washington D.C. Spingold.

 
At the time we were in a close match against an Australian/British team and this deal was live on BBO:

Vul: N-S Dir: West	A 7 4 A K Q 10 5 4 3 A 10 2
Q J 8 9 6 10 9 8 7 8 7 6 5		K 10 3 2 J 8 4 2 K Q 2 K 3
	9 6 5 7 5 3 A J 6 Q J 9 4

West		North	East	South
Larry		ENGLAND	David	ENGLAND
Pass		1	Pass	1NT
Pass		2NT	Pass	3NT
Pass		Pass	Pass

Our opponents were playing weak notrumps and 4-card majors (a very common British system). At the other table, our teammates were playing Standard American and North opened 1NT (15-17) which was followed by 3 passes. Since 1NT made easily (with overtricks), a large swing was at stake, depending on whether or not 3NT by South could make at our table.

I considered a spade lead, but opted instead for my diamond sequence. David put up his Q at trick one. Are you betting on declarer or the defense?

Declarer won the A and advanced the Q. What happens after David wins his K?

In notrump, we count winners. Declarer has 3 club tricks, 3 heart tricks, plus the A and A -- that's 8.

So, what should David do upon winning his K? Anything other than a spade switch allows declarer to set up the J for the 9th trick. So, let's assume David finds a spade switch. On general principles, declarer will duck the first 2 spades and win the third round with the ace. Then, the clubs are cashed. What can David throw? A little diamond is easy, but the fourth round of clubs will destroy his hand. He can't throw  a heart or a high diamond, so he has to throw the 13th spade. Now, a good declarer will lead to the A and play a diamond. He knows that East must have the K (or he would have continued diamonds earlier). East will have to win the K and concede the rest.

So, are you betting on declarer?

The title of the article is a clue.

David followed general principles of not winning his K on the first round of the suit. He ducked smoothly!

Of course, declarer repeated the finesse. Disaster!!

David won his (now bare) K and shifted accurately to diamonds. He played the K and another diamond. This gave declarer the J, but the clubs were dead. Declarer could take dummy's A, but had no way back to the long club. Declarer's only chance was a heart break, but after the ace-king-queen, the hand was over--down one. Our team won 6 IMPs instead of losing 10.

David didn't know at the time exactly what ducking the K would accomplish, but it was a good time to follow general principles.