In this game white played the opening passively so the tempo I lost with 1...a5 didn't mean much. But, what made this game somewhat interesting was the position after white's 31st move. White, who was completely lost anyway, thought he had a mate. He sent the move, which he had prepared by his previous move, immediately and congratulated me on having played a good game. After I retreated the B to f8 he spent a couple of minutes on his next move so I knew it took him by surprise.
What he overlooked was a backward move. Afek and Neiman wrote an interesting book called Invisible Chess Moves in which they stated that frequently uncomplicated wins simply do not enter our minds and even strong GMs suffer from blind spots; sometimes even both players fail to see the opportunity that is right in front of their eyes.
They discovered there are reasons why our brain discards certain ideas and one of the chapters is titled Backward Moves. C.J.S. Purdy also once observed that the hardest moves to see are backward moves, especially long ones and N moves. That's because we are trained to look for aggressive moves and such forcing moves usually mean advancing. When it comes to defense, we are usually looking for counterattack and that also usually entails advances. Somehow in our minds retreating or playing backward moves is not an option we even consider. That's what happened to white...he didn't consider the B retreat that defended against the mate.
Sometimes we fixate on an idea and don't see the obvious. I recently read an article on “design fixation” in which it was pointed out that sometimes your first idea is not the best one. But you might fixate on it especially if the idea has worked before. It might also happen because we are set in our ways, we experience tunnel vision, regurgitate an old idea or are blinded to alternatives. It happens not only to design engineers but it happens to chess players, too.