Source: ACBL
South was faced with a choice at his first turn in the auction. He could have made a takeout double, but he chose 1NT, which showed the value of his hand. North raised to 3NT, and West led the 
2. South won his ace and went to dummy with the 
A.
East followed with the queen, which gave South three spade tricks. Assuming the club finesse wins, South has nine tricks. So South led the 
J for a finesse and West won. East apparently had a lousy opener.
For the record, what does East have? If he has all of the remaining points, he started with the Q, the Q J, and the 
A Q. That’s 11 points. Not much of an opening bid. Perhaps his shape compensates a bit? We’ll see.
West continued with the 10. Given the bidding, West obviously doesn’t have any more hearts, so his spade play is safe. Sort of. What now?
You have eight sure winners so another must come from diamonds or hearts. Since East has the rest of the heart suit, it looks like diamonds has to be the source of trick nine. Can you get a trick from diamonds if East has the ace and queen?
You don’t need to lead a diamond now You can afford to cash your black-suit winners first. When you do, you learn that East began with the singleton Q and two clubs. East has exactly five hearts, so he must have started with five diamonds.
Here is where counting comes into play. When you finish running spades and clubs, eight tricks will have been played: three spades, one heart and four clubs. Everyone has five cards left. If you watched East’s discards, you will know which five he has. Did he come down to three hearts and two diamonds? Or did he come down to four hearts and one diamond?
What should South do in each of these cases?
If East has three hearts and two dia-monds left, lead hearts and give East the lead with a heart. He will have to lead a diamond to dummy’s king at the end. Nine tricks.
If East has four hearts and one diamond left, you know he has the singleton A. You can lead a dia-mond, ducking it to East’s stiff ace. Again, you have nine tricks.
Here is the complete deal:
Now that you can see all four hands, you can judge if the defense was okay. In fact, it wasn’t. If West, when he won the Q, had switched to the 10, East would win the queen and go back to hearts. After this sequence, South would have no recourse. You can decide for yourself if West should have gotten this one right.
From his perspective, East has opened a very weak hand and the actual East construction is about the only excuse for an opening bid that he can have. West’s play of the 10 was unlikely to work and West should have taken a few seconds to decide if the «safe» play of the 10 was best.