Cy the Cynic says that all of us are fools for five minutes or so a day. Wisdom is when we don't exceed the limit.
Against South's game, West led the ten of spades, and East took the jack and king and led the ace. South shrugged and ruffed with the queen of trumps, and West overruffed with the king and led a club.
South took dummy's ace and still had a chance, but he played East, who had opened the bidding, for the queen of diamonds: South cashed the ace and let the jack ride, and West's queen won. Down one.
"I am the only player in the world who could lose a trump trick with that holding - and then misguess in diamonds too," South growled.
It seems the deal arose when South was having his daily five minutes. To succeed for sure, South ruffs the third spade with the ace of trumps. He takes the ace of clubs, ruffs dummy's jack and exits with a trump. The defender who wins is end-played: He must lead a diamond or concede a ruff-sluff, and South is safe.
You hold: Q 6 4 T 10 9 6 5 3 A J 7 A J. Your partner opens one heart, and you respond 2NT (an artificial forcing raise). He bids three diamonds (conventionally showing a singleton). What do you say?
A: Since your ace of diamonds is perfect opposite partner's shortness, slam is possible even if he has minimum high-card values. Give him A J 10, A Q 8 7 2, 3, K 6 5 2. Mark time with a bid of three hearts, leaving room for partner to cue-bid the ace of spades.
East dealer
Both sides vulnerable

Q 6 4
T 10 9 6 5 3
A J 7

10 5 A K J 9 8 2
T K T None
Q 8 4 2 9 6 3
Q 7 6 5 3 2 K 10 9 4

7 3
T A Q J 8 7 4 2
K 10 5

East South West North
1 2 T Pass 4 T
All Pass

Opening lead - 10