This means that you have to lose tricks before you win them.
Case in point: North is dealing, with no one vulnerable:
S Q J 10 6 5
H J 10 3
D J 4
C A 9 6
S K 4 3 S A 7 2
H 9 8 4 H 7 2
D 10 8 3 2 D Q 9 7 5
C K 8 4 C Q 10 5 3
S 9 8
H A K Q 6 5
D A K 6
C J 7
The bidding proceeded as follows:
North East South West
Pass Pass 1NT Pass
2H• Pass 2S Pass
3NT All Pass
• Transfer to spades showing 5+
Opening lead: diamond 10
Granted, some pairs were playing in 4H, which will make if you can throw a club loser on a spade winner. In any case, the principle of building spade winners also applies in 3NT.
The opening lead went 10, jack, queen, king. Declarer then cashed five hearts before finally leading spades. East won with the ace and knocked out dummy’s club-ace entry. With spades never established, South went down one.
Before playing a single card, declarer should count up sure tricks: five hearts, two diamonds and one club for eight. The most logical suit for a ninth trick is spades. Therefore, lead one at Trick Two.
Let’s say East wins with the ace and knocks out the last diamond stopper. South will drive out West’s spade king. The defenders can cash two diamonds and lead a club, but it will be too late. South will make five hearts, two diamonds, one spade and one club for nine tricks.
East-West can complicate things if East switches to clubs at Trick Three, but North-South still have a way home. When West plays the king — always play the lowest card possible — you can be sure East has the queen-10 and your jack is safe. Therefore, win with the ace and continue on your merry way.
If West wins the first spade lead and returns a club, duck. If East wins the queen and returns a club you know she does not have the king so you play low. If West wins the king, your jack is good. If West has the 10 and plays it, let him hold it and win the third round.
By any measure, South makes the contract by creating new tricks instead of cashing old ones.