There are exceptions to every rule, including the rule about covering an honor with an honor. About 95% of the time, it’s right to cover a lone honor with your honor. However, the following two deals fall into the 5% category. The first one comes from the second final session of the NAP Flight A:
I was North, and I led the 10. Declarer won the singleton king in dummy and played a club to the jack and then the K. This should have told me that declarer was trying to keep South off lead. Declarer next led the Q. Because of my diamond holding, I reflexively covered the queen. I shouldn’t have done this, however, because declarer can’t afford to lose a trick to South. True, if declarer finesses, I have cost myself a trick, but double-dummy it’s easy to see that declarer was just fishing for an overtrick. Even single-dummy, I should have declined to cover.
There was a similar theme on this deal from the second final session of the Platinum Pairs:
East opened 2NT and West bid 3NT, ending the auction. South led the 2. Declarer won dummy’s 10 and led the J. I feel that North should draw a strong inference that declarer is off the whole heart suit. So if North doesn’t cover, declarer will not finesse. I was the guilty party on the first deal. The guilty party on the second deal will remain anonymous.