When I was 9, my parents, my brother and I house-sat for a couple who lived on a lakeside lot. This family happened to have a Nintendo with a copy of Super Mario Brother 3. My parents didn't want us to waste our time playing it when there was so much natural beauty to behold. They had a point, of course, but my brother and I still set our alarm clocks for absurdly early hours so that we could sneak down to play it. Every day for two weeks, we would get to the same exact place in the game.
...and then I beat it. Shouts of pure, unadulterated joy woke my parents up.
The rest of world 8 (which only really starts after the fast ship) was crazy hard, and it kicked my ass, so we didn't end up beating SMB3 that week, but more than maybe any other moment in gaming, this one got me hooked.