Lessons From Fagernes V

MY round-five game reached the following position.

What should White play?

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The position arises from the Exchange Variation of the Queen's Gambit Declined. The only slightly unusual feature is that the black dark-square bishop is on d6 rather than performing its more-normal role of breaking the pin on e7.

This apparently minor difference becomes huge if, as 20 times in ChessBase's 2023 Mega database, White continues 11.0-0?

This has been played by two players rated in the 2600s, two rated in the 2400s, three rated in the 2300s, two rated in the 2200s and two rated in the 2100s.

One of the remaining nine games was played at the 1966 Olympiad in Havana, ie before the world chess federation Fide adopted Arpad Elo's rating system, so it seems the mistake is particularly attractive to relatively strong players.

The reason it is a mistake is Black can play the Greek Gift sacrifice, ie 11...Bxh2+!. although five players, including one rated 2491, appear to have failed to spot this opportunity, or at least rejected it for a spurious reason.

After 12.Kxh2 Ng4+ 13.Kg3 Black has 13...g5, which gives a large advantage.

LESSON: apparently minor differences can make major changes. If, in the first diagram, whites, when considering castling, had asked themselves what captures would black then have, only two would have been possible: the clearly bad ...Rxe3 and the alarm-bell ringing ...Bxh2+. It is hard to believe anyone, especially a titled player, would play 11.0-0? if such a basic check had been made.