Last night, I did a straight up reality check- I looked down at my hands in the middle of a non lucid dream, and saw that my left hand had only three fingers and a thumb. But I didn't connect the dots and see that that means it's a dream. I assumed it was part of a game (in the dream I had just started up a video game, and the room I was in changed to match the game. Well it didn't but in my dream head I thought that that's how games worked).

Shouldn't this still have worked though? Be it a false reality or a game, shouldn't the reality check still worked? I'm not too mad, it's a good sign that I'm getting somewhere, but still, why didn't it work? Are reality checks not 100% fool proof?