Way before it happened? I only saw this movie for the first time not too long ago, and had no prior knowledge of it other than Brad Pitt was in it and that it involved an underground fight club. But I kinda figured out the twist roughly halfway through, maybe a little more. Or I correctly guessed the twist, more accurately.
Now don't get me wrong, I enjoyed the movie. I enjoyed Shutter Island a lot too, but I saw that ending coming a mile away. Just keep hearing how this movie is referenced a lot when discussing "blow your mind" twists and wanted to see how many others solved it before the reveal. Because I can say my friends we're hugely pissed I exclaimed what the reveal would be in the middle of the movie lol.