I might be getting the details wrong because it's been a long time, but I think were was a sort-of stuck point in The 7th Guest. When you're stuck on a puzzle, you can check a hint book in the library, and if you check it 3 times, it'll auto-solve the puzzle for you. There's some kind of limitation that I forget, like you can only auto-solve a certain number of times, or you need to legitimately solve a certain number of puzzles. But if you reach that limit before solving the "Microscope" puzzle then you may very well be screwed, because the A.I. opponent is nearly impossible to beat. In fact, at the time of the game's release, the lead designer had never been able to beat it.