The opening is a Caro-Kann Classical, with White choosing a relatively non-threatening sideline on move 7. Black goes astray strategically starting on move 10 with the errant plan of castling queenside. In the old (pre-1980s) Classical variation, this was in fact Black's main idea and considered safe if leading to unambitious positions. In this game, however, Black ignores the actual board situation to implement this idea, leaving White with a strategically won game as early as move 13. Black has no counterplay and White's forces are already ideally lined up against Black's king position. Some nice tactics for White end the game quickly after he ratchets up the pressure.
Black's main errors, from my point of view:
- Making the all-too-common amateur mistake of deciding to change your openings in a game because of a "bright idea" at the board. I had never played the queenside castling variation in a tournament game, despite having studied it superficially. At the time I thought it was "safer" and was proven wrong.
- Not calculating the consequences of my decision and relying on the current visual impression of the board. Looking ahead 2-3 moves would have (or should have) revealed that Black had major problems in this line. The position after move 12 for White is clearly unfavorable for Black.
- The tactical error on move 17. It combines some features of a counting error, in which the player doesn't visualize properly the results of a series of exchanges on a square, and missing the eventual skewer. At the time, I was prone to counting errors and I believe this was the root of the problem, i.e. not being able to visualize the final result on the board and therefore not seeing White's Bf4 threat in time.