This is very true. I remember a game on Theta Passage that had been very intense, but I got the upper hand and it seemed like it was all over, to the extent that my opponent said GG.
So I took my foot off the gas, he somehow survived, the game went on ten more minutes and I lost. I wonder if him saying GG was a ploy to make me back off. I doubt it in that case, but I think it's an interesting last-ditch tactic if you can get away with it.