I rarely restart a game if I'm heavily invested in it. Though, I did once when I found out that I ended up stuck and couldn't advance any further in the story/game. This happened once in Wild ARMs 2. I was far in the game, but I ended up stuck on the world map, because I didn't do something I needed to do. I even looked up in a walkthrough and found out that I completely skipped an important part. I had to restart the game just so I won't skip that. :U