Sometimes you're handling the main quest and a game will throw in some sort of diversion for your entertainment. This minigame, sidequest, or secondary story is so absolutely addictive, interesting, or just plain fun that you'll completely forget about the main story altogether. Don't worry too much about it. This isn't absolutely limited to videogames either. Many websites have so many nifty things going on that you don't even care about the main site at all. These are times when the main story or quest gets derailed by what you can do on the side.