I do this way too much. I will play a game for a while and then hit one point, maybe a challenge that I need to take a break from, and then time starts passing and before I know it I haven't played the game for so long and it makes more sense to start over. Or I will just want to play some other game for a while and the same happens. I rarely actually finish a game completely, lol (my signature will attest to that, as I've only actually completed 3 Zelda titles, while I've actually tried out/played a lot of them). Some games I absolutely intend to go back to and finish, while some games I also quit with the knowledge that I will not go back to complete (not just games I don't like either, but just games where I just want to continue past a certain point).
With Zelda titles it's Twilight Princess, Majora's Mask and Skyward Sword (and Spirit Tracks, but I haven't restarted it, just paused it before finishing what I think is the last dungeon) - I think I will continue past the current point somewhere down the line with TP and MM (especially with MM3D coming out) and I am hopeful about that because I did go back to WW and not only completed it, but also 100%-ed it. I'm not so sure about SS because of the Silent Realms and motion controls issues. Who knows, though.
I also really want to finish Super Mario Bros 3 at some point. I seriously love that game, but I still haven't managed to beat the 8th world, keep wasting upgrades on falling into pits and such in the levels (while the tanks and challenges are things I get by without much trouble). And I've restarted it more times than I can count.