How often does this occur? Perhaps more frequently than you may think.
In my game yesterday, in a losing position, I wondered momentarily if a threefold repetition had occurred, but convinced myself it needed another move, so didn’t claim the draw. Back home, my computer told me otherwise. As I went on to lose the game, I was somewhat annoyed at myself for not getting this right. I just didn’t take enough time to work it out properly.
This was the first position (of three):
My opponent (White) now played 42. Bd7 and the game continued 42… Kd6 43. Bb5 Ke5 (2nd repetition) 44. Bd3 Kd4 45. Bb5. At this point I should have written down my intended reply, stopped the clock and claimed the game (as per FIDE Rule 9.2). If 45… Ke5 the above position will have been repeated three times!
In my hassled state of mind (in time-trouble as usual), I mistakenly thought the position had only occurred twice. I played 45… Ke5, didn’t claim, and my opponent replied 46. Kh5, winning.
I wonder if anyone else has experienced this, or had similar ‘mind-blanks’?
(Rule 9.2 states:
The game is drawn upon a correct claim by the player having the move, when the same position, for at least the third time (not necessarily by a repetition of moves) is about to appear, if he first writes his move on his scoresheet and declares to the arbiter his intention to make this move…)