You Don't Wanna Help Your Opponent

J 9 2
8 5 4
K 8 2
10 8 7 2
10 8 3 6 4
J 6 A 9 3 2
A Q 4 J 9 7 6 5
K Q J 9 6 3
A K Q 7 5
K Q 10 7
10 3 Contract: 2 spades
A 5 Opening lead: K of clubs

When you lead a suit declarer would dearly like to lead, that's the equivalent of an entry for him. And you don't wanna do that -- well, by and large. You're supposed to make it difficult for your opponents.
In the above contract, we were only in two spades, where we were entitled to an overtrick, but a careless or kindly defender allowed us two overtricks. And who knows, but next time we might be a shade overbid in game, and then it's terribly expensive. I took the opening lead with the ace of clubs, drew one round of trump with the ace and then went to the jack. Why to the jack instead of drawing three quick rounds, as I could easily have done? Well, it was the 9 of spades that prompted that action, for I was looking for a ten doubleton to fall, for I do need entries so as to lead twice toward my heart honors.
How many do I need? Well, of course I don't know. If RHO has A J tight in hearts, I only need one. If A J low, I need two, and as the cards actually lie, I need three. And I wound up with three, the middle one coming from LHO. At trick four, I led to my heart honors, East going low, up goes the king. I drew the last round of trump, and now my only entry remaining, and that wasn't certain, was the king of diamonds. So I led a low diamond. Up went the ace on my left, and now came the jack of hearts!
I didn't mind that a bit. I now went to the king of diamonds and led toward my guarded 10 of hearts and had a third trick there, losing only one club, one diamond and one heart. Well, gosh, I could have finessed the 9 of spades, no? Then I would have had the entries I needed. Another way I could have made 10 tricks on my own steam would have been by laying down the king of hearts at trick two. If East wins, even if they wipe out my king of diamonds entry, I can cash the second heart honor after two trump leads by top cards in the closed hand, then go to dummy with the jack of spades and lead toward my 10 7. If East ducks, then he can't wipe out the king of diamonds, so I take 3 rounds of trump ending in dummy and lead toward my Q 10 7. If he ducks again, I win with queen, and now again, go to the king of diamonds to lead toward the 10 7.
But these are pie-in-the-sky hindsight solutions. You've got to remember that declarer can't see the layout of the cards all that clearly. That's why he'll make unwise choices from time to time. Finessing the 9 of spades doesn't have all that much appeal when I hold the top four trump, and as for playing the hearts in the manner described above, I didn't even see it, including being able to handle both a duck of the king and a capture, until I had looked at the whole hand. (Finessing the 9 of spades still has no appeal, even though I can see it would have worked. As for the hearts, I'm wondering if I should have seen that line.)
So you have to remember that declarers are very fallible creatures too. They can't see any more cards than you can. Yes, there was a way, indeed, there were two ways I could have made 10 tricks without help, I had not found either, and it's West task not to solve the hand for me. After taking his ace of diamonds, West cashed the queen of clubs, and I had the suspicion that he didn't want to continue clubs since that would establish the 10. But he sure had an easy out in diamonds. Indeed, if he'd just ducked my diamond lead, he could then lead clubs with impunity. The jack of hearts that came sailing out was a pleasant surprise I wasn't entitled to.