Sometimes not following general rules of bridge is better
You can't play bridge by rote and expect to get good results. A basic knowledge of general rules is certainly helpful, but occasionally a situation arises where following the general rule is clearly wrong and where something else should be done instead.
Consider this deal where West led the K-A and another heart, East ruffing the third heart. East returned a diamond, and South had to take the rest of the tricks to make the contract.
He won East's diamond with the king, drew trumps and then played the king and another club, planning to finesse dummy's jack. But West showed out on the second club, and South had to go down one.
Declarer's method of play appears normal, and the outcome -- down one -- seems preordained. But, upon reflection, it is easy to prove that South misplayed the hand.
Declarer learned at trick two that West had started with six hearts, and later learned that West had started with three spades. Before touching the clubs, he next should have led a diamond to dummy's ace and ruffed a diamond.
This search-and-discovery mission would have revealed that West also had started with at least three diamonds, leaving him with at most one club.
Leading the K-x of clubs at this point was therefore likely to be a futile exercise, even though it was the usual way of handling this combination. South's best chance, knowing that West had at most a singleton club -- hopefully the queen or ten -- was to start the suit by leading the four to dummy's ace. After West's ten appears, declarer wins with the ace and returns the three to his nine with a 100 percent certainty that the nine will win the trick.