The Avoidance Play

K J 9 6 3
5
K J 9
Q J 8 3
8 5 4 Q 7 2
A J 7 3 Q 9 8 2
Q 2 10 8 5 4 3
A 7 5 4 9
A 10
K 10 6 4
A 7 6 Contract: 3 no trump
K 10 6 2 Opening lead: 3 of hearts

Two declarers with the same opening lead in the same contract got such disparate results as one going down a trick, the other making 6! And in each case, it was the spade suit that did in the low-scoring side.
On that opening lead, East goes up with the Q and declarer wins with the K. The principal danger here, of course, is East on lead. A heart through South's tenuous holding could mean a not too improbable 4 heart winners on a 5-3 break. Can you avoid the club suit and win on finesses? Well, by golly, it's not only mathematically possible, but the cards are right for it. All you have to do is pick up 3 diamond tricks, the queen falling easily, then finesse against the queen of spades the right way and not least find the queen guarded no more than twice. That would take a lotta luck: friendly diamonds, a successful spade hook and 3-3 spades! But the cards happen to be there for the taking!
Another way is to take your chances on the ace of clubs, which even if with East won't necessarily spell the defeat of your contract, i.e., if hearts are splitting 4-4. And if it's not with East, you've got a guaranteed contract. You merely have to keep East out of the lead as you lose at worst two hearts, a club and a spade. Indeed, chancing the A of clubs looks far safer than expecting all that luck with the diamonds and the spade finesse and distribution. Or in a positive count, you've got three clubs winners, three diamonds and two spades and a heart. And if West doesn't cash out his two hearts? Well, that's obviously what happened with the declarer who made 6! Declarer can manufacture a third spade by going to dummy, finessing the 10 and whether it holds or not, unblock the ace and get back to dummy for the K and J. Which leads to two more spades. Which is to say five spades, three diamonds, three clubs and a heart.
It's not hindsight that demands that you take the spade hook through East. It's called an "Avoidance" play.
Hence, at trick two, I would lay down the king of clubs and note with pleasure that East follows with the 9. That doesn't mean East doesn't have the ace (assuming West ducked), for he can see I'll continue the suit with the Q J showing, but it beats seeing the ace. Now a lead to the queen of clubs, whether taken by West or not, will put me in a path to two entries in clubs alone to first take the spade hook through East, then cash the ace of spades and get back with either a club or diamond.
The declarer who went down finessed the 10 of spades into East, and I need hardly relate how the defense got 5 tricks. (Three hearts, a club and a spade.) Did the declarer who made 6 make the right avoidance play as West failed to cash his A J of hearts? Well, not exactly. His LHO came to his rescue. At trick 2, declarer went to dummy with the jack of clubs, came back to the 10, which held and finally got that ace on the third round. And now West led the 5 of spades. That took care of that hand. Free finesse, anyone? Declarer could now run 5 spades, 3 clubs, 3 diamonds and the heart. West should have gotten out with a safe club lead -- well perhaps after cashing two hearts -- following his win with his ace of clubs. Declarer now has no more entries in that suit, and must hop on the spade suit for an overtrick before using up diamond entries.
A lot of "if's", but that's part of bridge, and given the ace of clubs with West, you can't be beat. There's all the difference in the world between the 10 of hearts and the 9, there. And declarer had better take advantage of such lucky layouts because your opponents will be doing so.
A safe club out by West doesn't hurt declarer here, for with the queens as they are, he now has two entries and needs only one. But if the queens were reversed, he'd have one entry and need two. So I don't know that he was prepared to take an avoidance play.