What was the hardest video game that you managed to beat? How long did it take you from when you first started it to when you finally finished it?

For me, way back when I was a youngster still in elementary school, I managed to beat Super Mario Bros: The Lost Levels (Japan's Super Mario Bros. 2) on the SNES's Super Mario All-Stars package. I didn't think that game was all that difficult originally (since I was so used to playing the first Super Mario Bros. a lot on the NES that I had at the time), but with more recent playings (including the version found on Super Mario Bros. Deluxe and the Virtual Console release (the first time the original FDS version was released outside of Japan) especially), I found it so difficult that I had to restore from a saved restore point multiple times in the same level in order to beat it. Super Mario Bros. 3, despite what some people say, is even worse in this regard, and I don't remember ever beating that one.