I recently read about his deal from the 2008 Senior World Championships, and it surprised me.

East held:  

 A109864  
 J62  
 8  
 A94

In a team match, neither side vulnerable, his LHO (South) opened 1. This was raised to 2 (inverted-showing 10+ HCP). He ventured 2 and opener tried for game with 3. Partner raised to 3 and RHO jumped to 5 and bought it there. Partner leads the 2 and you see:

Vul:None Dlr: South	5  AQ3  A6542  Q652
		A109864  J62  8  A94

Against suits, this pair was playing low from odd and 3rd-best from even. This method is popular among experts to help them count out the hand. Here, you know partner started with either 3 or 5 spades (with 4, he would have led his 3rd-best). You play your ace, declarer following with the queen. And now?

I always preach that the most important consideration on defense is to decide whether to go passive or aggressive. What's your play at trick 2?

There is danger in playing another spade. It looks like partner started with 5, and a spade would give a ruff-and-sluff. A trump could be safe, but not if partner started with Qxx. Here, passive would be a low heart. How could it hurt? No matter who has the king, this won't give away a trick.

The most tempting play is the A (that is what most inexperienced players would play -- "a trick is a trick)". However, that is a very dangerous play (either the ace or an underlead). The reason to make such a shift ("aggressive") would be if you were afraid that if you didn't, it would go away. If there is nothing in dummy on which to throw things (as here), then go passive. The expert East player, inexplicably laid down the A at trick two. This was the Real Deal:

Vul:None Dlr: South	5  AQ3  A6542  Q652
KJ732  1087  107  J73		A109864  J62  8  A94
	Q  K854  KQJ93  K108

No surprise, this was a disastrous decision. Declarer soon claimed 11 tricks and +400. Had East made a passive shift (either red suit would do), in the goodness of time, declarer would likely lose 2 clubs tricks (yes, double-dummy, he can make by leading the 10 from hand, a "backwards finesse"). Of course, if dummy ever leads a low club, East has to follow second-hand low.

East had committed what I teach is the most common error on defense--wasting your aces to capture only low cards. Or, as the way I sarcastically put it in my classes, playing the A means "one trick for you, two tricks for them."