Even the world's best have their bad moments. A newly-minted ACBL Hall-of-Famer (remaining nameless) had one on this deal from the 2019 Vanderbilt Teams. He held:

109
KQ107532
94
54

At unfavorable vulnerability, his partner opened with a strong club. RHO showed minors and eventually the opponents sacrificed in 5 against 4. This propelled South into 5 with the J lead on this layout:

AQ54 AJ K7 A10762
109 KQ107532 94 54

If both the K and A are with LHO, all will be good. Declarer won the A and drew trump ending in hand (they were 2-2). He led another club (all following), losing to RHO's 9 and a spade was returned to the 10, jack and queen. Declarer ruffed a club (LHO showed out) and ran some trumps. As you can see from the Real Deal, this was down 1:

Vul:N-S Dlr: West	AQ54 AJ K7 A10762
KJ83 86 J8652 J8					762 94 AQ103 KQ93
				109 KQ107532 94 54

In addition to the club trick lost, declarer had to lose 2 diamonds.

Where did he go wrong?

He made an error that encompasses probably the most important theme in trump-suit contracts: "Should I draw trump?" The answer here should have been "NO!". Why? Dummy's AJ are precious entries.

Declarer should win the A and return a club (dummy's 10, so that West can't possibly win) at trick 2. Yes, East showed minors, but at this vulnerability, against a strong club, he could easily be only 4-4 or 5-4. If clubs turned out to be 5-1, nothing would be lost--declarer could still hope the K and A were right. When in fact clubs turn out to be 4-2, there is no need for both finesses to work.

East can win, but there are still plenty of dummy entries. Declarer can use them to ruff a 3rd club and then a 4th club (trumping high each time). Once trump are drawn, he can reach dummy (presumably guessing to take a spade finesse) to throw a diamond on the 5th club. All he should lose is a trick in each minor for +650.

At the other table South was allowed to play in 4. A diamond was led, which held the contract to 10 tricks.