A tough hand, doing 10 declarers in. It would be a piece of cake on 3-2 hearts, but you don't get 3-2 hearts, for which you should be glad, q.v. Should the defense hit spades with three tricks, they would willy-nilly hand the contract over, for declarer ruffs low and can now have no trouble drawing trump in four rounds for: 5 heart winners, three diamonds and two clubs. But everybody was getting the J of diamonds opening lead, and that allowed declarer to go astray.
First we count: barring 5-0 trump, declarer has 9 top winners. Not quite enough. A tenth might come from a spade ruff, as just referred to. It might also come from the fourth round of clubs if they're splitting 3-2. You might even handle a 4-1 club split if the honors sit before the 10, though bear in mind that entries are at a premium. Anyway, declarer starts with two rounds of hearts, and -- eek! It's not going to be an apple-pie hand. First look at the dangers besetting us if we try to lose two spades so as to pick up a ruff. East wins the first round and leads a trump and does the same when you lose the second round of spades. Yikes! Now you can't benefit from 3-2 clubs, since you're wide open in spades! And you didn't even get that ruff! Or suppose East wins the first round of spades and leads a diamond and West wins the second round and leads a diamond. Could diamonds possibly split 6-2? So even if you hit spades before even one round of trump, you're in trouble on diamond leads.
There is, to be sure, one other line of attack, and that is to bank on 3-2 clubs, losing a club. If the suit is 3-2, you're safe losing the first round, and if not, you're going to have trouble with it eventually, anyway. Indeed, this looks to be the only safe line after two rounds of trump. The defense now might switch to three rounds of spades, for it wouldn't hurt them, but you'd have communication. You'd be all right if you took the first two rounds of trump with the A Q. Now you'd ruff low and lead to the K J of trump. Even if you took one round of trump with the A, another with the K, you'd be able to ruff a third round spade low, cash the Q of trump, and now you'd have the K of clubs for an entry to the last trump and a running of your winners.
The first declarer took the opening diamond lead with the ace and led to the K of hearts and back to the A. That was a mistake, i.e., the lead to the K. The first two rounds of trump should come from the A Q. That's because if you lose a club to establish a 10th trick there and the defense now switches to a spade attack, the heart suit will be blocked, which happened to several declarers. You'll be looking at the Q of trump in one hand (after ruffing a spade) and J 8 in the other, and no way to reach the J to draw the last trump. [years later: not sure what I meant, since declarer would have the K of clubs. Had those declarers possibly cashed three rounds of clubs, upon seeing the bad trump break, which they couldn't afford with all trump out? That's the only thing that would warrant my statement of having no way to reach the J of hearts.]
Anyway, after seeing the bad break with the second round of trump, declarer tried to get a spade ruff, losing the next trick to the Q of spades, taking a heart to the Q, losing the next lead to the K of spades, winning a club lead with the K in dummy, ruffing a spade. The problem is that now he has no entry to the J of hearts. He cashed the K of diamonds, then tried to cash the Q of diamonds, but it was ruffed, a spade lead was ruffed with dummy's last trump, the A of clubs was cashed and declarer had to surrender a club trick to the Q.
You might note that E can win each spade lead and lead a trump, also, leaving none for ruffing purposes. It was too late for declarer to try to shorten his spade holding for a ruff. He would have done far better simply to lose a club. It's no more dangerous to just lose that club than to cash the A K and then lose it. If the suit is splitting 4-1, you're in trouble either way, and if not, losing the club first gives you some flexibility in entries. Now if the defense hit three leads of spades, declarer ruffs, cashes the Q of trump, enters dummy with the K of clubs, draws the last trump and claims.
The next declarer got a club lead (the only defender who didn't lead the J of diamonds), taken with the K. Declarer would have done well to duck it, for he would soon have 10 top tricks only delayed a bit if the opponents shift to some rounds of spades. [The above reference to 3-2 clubs vs. 4-1 holds all the stronger for this declarer. He would have been one happy camper if he'd only ducked that lead.] He too took two rounds of trump, one with the K, which is going to be his undoing. Now he led a spade, taken with the Q, diamond to the A, another spade, taken with the K, cash the K of diamonds, play the Q of diamonds, ruffed, of course, and declarer still had to lose a trick to a club and to the A of spades. [I seem to have left something out: another spade, taken with the K, cash the K of diamonds. I guess that should read: another spade was won by West, who returned a diamond.]
Declarer Number 3: Here's one who got specifically hung up on taking the first round of trump with the K, instead of the first two with A Q. Second round did go to the Q, two top clubs cashed, diamond to the Q, lose a club to the Q, the defense now runs three spades, declarer ruffing the third round. Declarer now had the A of hearts, a top diamond and top club, opposite the J 8 of hearts, while East had a spade and two hearts. Hearts are blocked. Declarer can cash the A of trump, but cannot get to the J to draw East's last trump. Down one.
Number 4: Diamond to the A, three rounds of trump with the A, K and Q in that order and declarer now cashed the K of diamonds, tried the Q, which was ruffed, and he's going to wind up short a winner with that. His best hope after three rounds of trump would have been to lose a club. He would seem to be able to withstand a spade attack, having the K of clubs for communication draw the last trump, or have the last round of trump led. But it wasn't to be.
Number 5: Diamond to the A, A of hearts, heart to the K. Can't anyone simply cash A Q just by accident? Now the K of diamonds followed by the Q which was ruffed. Of course. Why the Q of diamonds? Declarer evidently wanted to shorten dummy's spades to give him 2-2, but why? He should want them to run three spade tricks (if only he'd led the A Q of trump). But the third round of diamonds has no rhyme or reason until trump are out. Down one. He still has to lose two spades and a club.
Number 6: This declarer was clearly and explicitly done in by taking one round of trump with the K. Diamond to the A, A of hearts, low to the K, cash K, the A of clubs, lose a club, A of spades, K of spades, J of spades, declarer ruffing, now looking at a blocked heart suit, the Q in one hand, J 8 in the other and no way to cash the two top trump to draw East's trump. Wouldn't declarer have preferred a low trump opposite K J? And is a 4-1 split so rare that you take no precautions against it?
Number 7: Diamond to the ace, A, then Q of trump led. Ha! The first one who did that. Now if only declarer would lose a club, which he'll have to do eventually anyway and which is no more dangerous than cashing the A K of clubs, where a 4-1 split would do you in in either case -- if he'd just lose a club, he'd be sitting pretty, able to handle a spade attack, able to run 10 winners if he doesn't get it (4 hearts, 3 diamonds, 3 clubs). But no, he didn't see it that way, for after cashing the right honors, he tried to induce a spade attack by leading a spade. Back came a diamond and he fell for it, continuing the suit into a 3rd round ruff. He was so close.
Number 8: Diamond to the A, K then Q of hearts, K then A of clubs, lose a club, three spade leads, forcing declarer to ruff and he too was looking at a blocked heart suit. The Q in one hand, J 8 in the other and no way to cash them separately.
Number 9: Diamond to the A, A, then Q of trump, followed by the K!, two top clubs, then lose a club, diamond back. Wait a minute! Is he going to make? He wasn't forced to ruff a spade. He can lead to the J of hearts, then back to the K of diamonds by way of the 4th round of clubs, except that . . . oooooh. He saved the 10 of clubs in dummy instead of saving a low club to lead to the 6. So with no entry back to the K of diamonds, he'd better cash it first, eh? Diamond K is ruffed. Down one.
Number 10: diamond to the A, cash the K, try to cash the Q! ! ! ! Why on earth try to run three diamonds, a suit chosen by the defense, before testing hearts when he might have found a very benign 3-2 split, making the hand a cakewalk. He was looking to get rid of a spade in dummy, but he can handle that, certainly on a 3-2 split and even on a 4-1 as outlined above. And so it goes.
J 10 3 
K J 8 2
A 4
K 10 4 2