I had the feeling that I'd entered this hand before, but I'm not sure where. When I looked at it recently, it seemed to have about 4 lessons to offer, and so this must be the best spot. Contract 6 no, deuce of hearts led. Counting winners, we see 5 spades (not a certainty until both opponents follow to the second round, but we'll start with that supposition), three hearts and three clubs, for eleven. So we need one more trick. Looking from declarer's viewpoint, we see two possibilities, to wit: that hearts split 3-3 and that the A of diamonds is onsides. Nor can we test them sequentially with complete safety. But of the two, testing hearts is far more attractive. If you test diamonds first, and the ace if offsides, you're down already and it won't matter how hearts split. If you test the hearts and they're unbalanced, you're outta luck if the long hearts lie with the A of diamonds on your right, but at least you have a 50% chance that the long hearts do not lie on your right, and if the A is onsides, you're still in clover. Of course, we can see that both possibilities would pan out for a 12th trick. So even a declarer who went for the most dangerous course would come out smelling like a rose. Then how come two declarers went down here? Ah, therein lie the lessons to ponder.
Opening lead taken in the closed hand with the ace. (The play of these two declarers was so similar that I had to check to see that I had two different ones, rather than one printed out twice.) Five spades are run, sluffing in dummy two diamonds and a heart. Now one declarer cashed out three clubs and two hearts, or in other words, starting with 11 tricks, she cashed 11 tricks and wound up with 11 tricks. The last two tricks were a club to West's 7, and a diamond to East's ace. The other declarer deviated a little: after five spades (sluffing a heart and two diamonds), and two clubs, declarer cashed a heart, led a diamond toward the K, East going up and shooting a club back to the Q. Declarer could cash the Q of hearts, but with no access to the K of diamonds now, lost the last trick to the club 7!
Well, where to begin? From trick one, they were both scuttling their chances, especially the second one. You have two heart honors in dummy, and one in the closed hand. If you don't have a clear grasp of how you're going to develop winners, don't you think it'd be wiser to use one of the honors where you have two, so as to retain the flexibility to move to either hand later in this suit, rather than restricting yourself to one-way traffic? (Elsewhere I have a hand where declarer has three top honors in one hand, one in the closed and allowed the opening lead to ride to the single honor, thereby scuttling her chances. It seems to be something of a bad habit, to let that opening lead ride while you're doing some thinking.)
The biggest lesson, however, the one that prompted me to enter this hand, was the run of the spade suit. If I've said it once, I've said it fifty times, don't run your best suit until you're ready to cash out. If it's balanced, you're removiing a lot of communication, and if it's unbalanced, you'll (probably) have as much trouble as the opponents or more finding suitable discards. I expect the motivation behind that common practice is the hope that the opponents will make a foolish, trick-giving mistake but it didn't happen on this valuable slam, and that's worth pondering. Here dummy can spare a club and a diamond and then is squeezed on the third round. A heart discard means you wipe out that potential, while a diamond discard means you won't have access to the K even if the A of diamonds is onsides. But then, since both potential winning paths would work, that alone wouldn't have queered the contract, except that . . .
Neither defender sluffed a club! Which turned out to be the setting trick in each case. Each one queered the contract by wiping out both the heart potential and the diamond. Now the 6 of clubs cannot possibly be a winner, except on a defensive error. Somebody has to have 4 or more clubs, and that somebody cannot possibily have all four under the six, since there are only four such cards in the deck, and declarer has one. Which brings us to the next lesson, which is do not count on defensive misplay when you have a viable path of your own. Even when you're right and get that misplay, it's not doing much for your bridge, and may even make a partner wince. Clubs cannot possibly split favorably vis-à-vis the 6, while hearts can split favorably vis-à-vis that 6.
I see this all the time. I see this al-l-l-l the time: declarers skeered that a risky play won't work put it off until it is too late to make their contract thought it would have worked. This is one of the many, many such cases. By postponing the risky play, declarer winds up ensuring that he'll experience that setting trick later. Why would anyone run spades, sluffing dummy's fourth heart instead of testing hearts first?