During the last few decades there has been a great focus on ‘new moves’ or ‘theoretical novelties’, with the implicit assumption that these dreaded creatures can strike us from a clear blue sky and cost us the game.
There have been cases of new moves causing havoc, but this needs considerable clarification. New moves, by definition, are simply moves that haven’t been played before. And they can also be old moves which didn’t find their way into the databases.
Are new moves usually better moves? Well let’s think about that for a moment. If a position has been played many times before, and by Grandmasters, would they all miss the best continuation? That seems unlikely.
A more likely scenario is that a player will be looking to throw his opponent on his own resources by playing something a bit different. Such innovations are unlikely to be better than the established moves, but that doesn’t stop them working.
Are new moves played deliberately, or can they sometimes be accidental? Well I know from my own experience that it’s possible to forget your intended opening variation and end up improvising. Now it could be that I’m particularly forgetful, but I suspect instead that I’m not the only one.
Here’s an example in which a future GM, Juan Manuel Bellon Lopez, plays a ‘theoretical novelty’ (according to my database) with 9…Nxd4, the established moves being 9…e6 and 9…Nb6. But unfortunately it loses a piece!