On many no trump hands declarer has to force out two defensive winners before he can run his tricks. It may be essential to force out those winners in the right order.
Usually the first assault has to be made on what is eventually going to be the danger hand.
Dealer South All Vul
 8 2 J 10 5 A 10 9 6 5 2 J 6 |
||
| Q 9 5 4 3 A 6 3 8 3 K 9 2 |
J 10 6 9 8 7 4 K 7 Q 7 4 3 |
|
| A K 7 K Q 2 Q J 4 A 10 8 5 |
The Auction:
| West | North | East | South |
| 1 |
|||
| Pass | 1 |
Pass | 2NT |
| Pass | 3NT | End |
Lead: 4
South holds off the first spade and wins the second. Now observe what happen if he makes the normal play of establishing his long suit first: a dimond finesse will lose to East, who will clear the spades; declarer will still need a trick from hearts and when West comes in with A he will make two more spades to defeat the contract.
After the play to the first two tricks has placed West with the long spades, South should play first on the suit where West may have the entry.
It is clear that West can be kept out the lead in diamonds, but not in hearts if he holds the Ace. At trick 3 South must lead a heart. West will probably hold off, to conserve his entry. Then South can turn to diamonds with his ninth trick assured.