The only way to be successful at bridge is to think ahead ....and plan ahead. My partner and I needed a couple tops to cement our number one position. I was dealt AKQ3....KQ7.....KQ107......A9, but my partner held a more modest 954...62....A942.....KQ62.
Six diamonds was a lay-down with 12 certain tricks, but I opted to take a punt at 6NT. However, with bad breaks there might only be ten tricks on top, However this became eleven, when East lead out the jack of diamonds at trick one. Now, by leading up to the king of hearts presumably taken by East with the Ace, I could take 8 tricks out of the first nine : 3 top spades, 4 diamonds and at trick nine, the Ace of clubs. This would leave a 4 card ending : me with 3.....Q7...(no diamonds).....9, and dummy with (no spades)... 6...(no diamonds)....KQ6. THE SQUEEZE WAS ON. East who started out with a 2-5-2-4 distribution was obviously holding 3 clubs to J108 and 1 decent heart. West who was clearly holding onto the boss spade, now only had room for 2 hearts and a club.
If now the 9 of clubs is played to dummy queen, with the king to follow. West is well and truly fixed : he must surrender the 10 of spades or the 8 of hearts. Slam made.......top well earned.
In other scenarios, the defenders are in similar trouble since between them they had to guard against 3 clubs winners, 2 heart winners and 1 spade winner, but each only had four cards to achieve this impossible goal. If East had the 3 clubs and the winning spade, then the queen of hearts at trick 10 squeezes him straightaway.