Count Winners, Count Losers

Q 6 3
J 8 4 2
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J 9 8 7 5 4
9 7 K 5
A 10 7 K 9 6 5 3
10 8 7 6 4 J 9 5
Q 10 3 K 6 2
A J 10 8 4 2
Q
A K Q 3 2 Contract: 6 spades
A Vul: No one. Opening Lead: anything

Only 8 out of 11 declarers in 6 spades made it. It's a lucky make, since the spade king can't be guarded more than once, or you're outta luck. But the luck is there in the cards, and declarer doesn't have to be lucky in choices. He only need count out his losers in the closed hand and see if he can find a winner in dummy for then, excepting one, which you can afford.
Here there is obviously nothing declarer can do about the heart loser. Clubs are taken care of, same with hearts past that unavoidable loser, in spades you'll be at the mercy of a finesse you can't do much about to avoid, which leaves you with two low diamonds. So if you wanna make the hand, or at least give yourself your best chance, you wanna ruff out those two low diamonds. That's not higher mathematics, and it's not beyond the capability of an average novice if you'll just stop and say, I've got to account for every card in this hand (here the closed hand, of course).
To be sure, there's one hitch, namely that diamonds could split 4-4, while the king might be guarded twice, in which case ruffing twice would spell an avoidable defeat. Anyway . . . Take the opening lead of a club, say, ruff a diamomd, play the Q of spades. Do not cash any top diamonds as some declarers are wont to do. You'll get those winners later. Those who got a cover here, as some did, had an unambiguous line to take. You know you've got the trump suit cooled (barring a 4-0 split, which you learn isn't so by the end of the trick). Ruff another diamond, club ruff to the closed hand, draw trump and claim. Without a cover, declarer is in a touch-and-go situation: which suit is going to split evenly: spades or diamonds? I don't think anyone can justly critique a declarer for guessing wrong. The only thing one might say is that declarer must play for one or the other to be true.