An ACBL Hall-of-Famer was guilty of letting emotions turn a poor result into a near bottom. This deal is from the 2025 Life Master Pairs Session 3:

In fourth seat, Vulnerable against not, South held: 

AKJ962

J43

AQ6

5.

After two passes, RHO opened 1.  This hand could start with a double and then bid spades, but the chosen overcall of 1 is probably mainstream. The opponents are now passing throughout and partner raises to 2. The high road (quite reasonable) would be 4, but this player settled for a natural game try of 3, and then honored the partner's lack of interest and passed 3. A diamond was led:

843  K108  K72  J1076
AKJ962 J43 AQ6 5

Partner doesn't have much, but those two red-suit kings (instead of club cards) are quite useful. Perhaps partner should have made a counter-try of 3? Perhaps we should have bid 4? Still, with 2 likely heart losers and a club, the game needs spades to come in.

Declarer won the diamond lead and banged down the high spades, finding them two-two. Sigh. Next came a lazy heart to the 10 and ace.  What was South's biggest crime? This was the real deal:

Vul:N-S Dlr: West	843  K108  K72  J1076
Q10  Q92  543  Q9842		75  A765  J1098  AK3
	AKJ962 J43 AQ6 5

Whether or not you agree with the bidding judgment, it was the lazy play of the heart suit that you should label "criminal." Sure, if West has a doubleton or singleton Q, low to the ten will work. But that would mean East started with 5 or 6 hearts--the same East who opened 1. The correct play in hearts is to start with the jack. If East has the AQ, nothing matters. But if West has the Q9 (as in the real deal), South loses only one heart trick (if West covers the jack, declarer later finesses against the 9). Making only 170 was roughly a 10% board. Salvaging 200 (for the second overtrick) would have gotten North-South up to almost average on the board. Once you are in your contract, you can't let emotions get the best of you. Taking his eye off the ball cost South nearly 1/2 a board.