Declarer let the opening lead ride to her ace, drew trump in three rounds and now led to the K of clubs, played the Q, which was captured by West, who now led a heart, which declarer ruffed in dummy. Down one! What else at that point? Declarer has no more trump in dummy for a second heart ruff, no entry to dummy after ruffing out the third round of spades.
This hand would obviously work very well as a dummy reversal, q.v. Your best side suit hits you in the face when dummy comes down. As soon as trump are out, you cash the A K of spades, breathe a sigh of relief when they split 3-2, ruff a spade and claim, conceding the A of clubs. But this declarer rushed to wipe out her club entries to those lovely spades, along with giving West a chance to wipe out that last trump entry with a heart lead.
How can anyone go after clubs before spades? You don't need to go after clubs. They're 3-3, a solid 3-3, and can be led from either hand. You don't need an entry to them, while you'll certainly need an entry to the long spades. Declarer actually would have been safe had the second club lead been toward the jack. If captured, she has an entry with the Q of clubs (or if West shoots back a club, then with dummy's last trump). If the J is not captured, there's nothing more for declarer to do with clubs, and in fact you've got an overtrick coming (i.e., if spades are now set up, allowing declarer to return to dummy on a trump entry and sluff the closed hand's remaining club). So it's not only why the club suit, but why take care to wipe out the honors in the hand where you'll need an entry?
Now hear this: in counting out a hand, you must account for every card in one hand or the other. So you want to make every card in dummy a winner, with the qualification that you'll have to lose one trick to the A of clubs. That's your primary task. Do not cash out top cards frivolously, i.e., without a positive reason, until you've done all you can for one hand or the other. There's just no reason to touch clubs until you've done all your housekekeeping, and I'll never understand if I live to be a 100 why it is such a common proclivity for declarers to rush to wipe out key entries for no good reason.
Could we not ruff just two hearts in the open hand, making every card in the closed hand accounted for? That would seem to simplify the hand. The problem is, you don't have a convenient re-entry to the closed hand with all that power! There is no re-entry in clubs (or at least the defense can inhibit a club re-entry). You can't use trump re-entries twice and ruff twice because you'd be chewing up honors needed to draw trump, setting up the 9! And yes, cashing two top spades and ruffing a spade would work, but if that's your shtik, thus establishing the spade suit, why not just forget about hearts and play a dummy reversal in the first place?
The curious thing is that if we had just one of dummy's heart honors in the closed hand for a spot card, or one of the spade honors in the closed hand or one more of the club honors in the closed hand -- any one of these three changes -- then it'd be a cakewalk to ruff a heart in dummy, come to the closed hand (delayed, perhaps, with a club lead), ruff another heart, cash a top diamond and then overtake a second diamond lead for finishing off trump. But you don't have one of those honors in the closed hand. You're playing a hand everyone else is playing, and a frank look at the entries invites setting up the hand with pul-lenty of entries, no? Yes, there's always the danger of 4-1 spades, but what's the alternative? I just pointed out above that a third round spade ruff offers your only re-entry after a second heart ruff, yes, aside from a tenuous, uncertain chance in clubs. So you're going to have to test spades anyway!
Indeed, it looks to me as though you could live with 4-1 spades as long as West has the ace of clubs! Take three rounds of trump (there are no more trump in dummy but you have the ace of hearts), cash the top spades, noting that someone shows out, and ruff a spade. Back on a club lead. It doesn't matter when West hops up with his ace. When you get in, you ruff another spade with the last trump on the hand! and lead another club. You don't need the ace of hearts as a winner, only as a stopper. And that's with 4-1 spades! So looking at all the entries to dummy -- a couple of club honors, three trump honors -- I would say declarer would find the hand much easier to play if he noted the scarcity of reliable entries to the closed hand and banked on those entries to dummy. Setting up the spades works before all trump are drawn and works after all trump are drawn, and even works on 4-1 spades after trump have been drawn by the location of the A of clubs.
I mulled it over for awhile and realized that I could have outlined a fairly safe way from declarer's viewpoint. Declarer should ruff the opening lead in dummy and cash two rounds of trump with dummy's honors. Now, if trump split 2-2, there's nothing to think about. You'll ruff that last heart loser in dummy (eventually) and claim, conceding the A of clubs. This spares you grief if spades are 4-1 and trump 2-2, and I shouldn't suggest a dummy reversal so quickly.
When you see that trump don't split so benignly, then you go for the spades. You're okay on any 3-2 split (you can ruff high if West has the last trump and shortage in spades). You can live on a 4-1 if the defender with the shortage is also the one now out of trump, regardless of who has the ace of clubs. That's because we still have a trump entry to dummy, by which we'll draw the last trump and ruff the fourth round of spades, and lead a club.
But on mulling that over, I think drawing the last trump and banking on West to hold the A of clubs (in the event of 4-1 spades) would be a tad safer than delaying the third round withdrawal. This has the advantage of eliminating dependency on who has the A of clubs, but the disadvantage of banking on two singletons in the same defender's hand! After all, the location of the A of clubs is a 50% chance, while the other chance doesn't seem near so likely.
But there's no 4-1 spade split, even if there is a 3-1 diamond, and the hand is a cakewalk if declarer takes a keen look at where adequate entries lie and plays to establish the hand with the most.