The psychology of completionism (or the lack thereof)

Anyone else out there like me?
 
Anyone else have trouble actually finishing nearly every game they own? I swear I'm almost at Vinny levels of collectionism/completionism, but I also refuse to actually finish the game, no matter how close I am.
 
Case in point. The lady and I bought Mario Galaxy 2 on launch day. We'd also bought Galaxy 1 on launch day 2 1/2 years ago. She had finished it (with about 70 stars) ages ago. I passed her star count, then continued to be all "I'm gonna get MORE stars before I finish it. Hell, I think I'll try for 120!"
 
I proceeded to put the game on the shelf for about 2 years, not touching it more than once or twice, maybe getting a half dozen more stars. Buying the sequel and not wanting to start it before finishing the original made me pop it back in and see the ending (weird existential ending for a Mario game, BTW).
 
And yeah, this is a pattern too often repeated, by me anyway. I refuse to actually let games end. Why must that be?
 
I have a great time playing them, but of the 40 or so games I own currently (trade and save pretty prequently), I'm maybe totally finished 15. Hell, all three modern Metroids have sat unfinished (all but for the final bosses) since a month after their respective releases.  Fallout 3 sat one mission from complete for more than a year until I picked up the GOTY edition.  Assaccin's Creed 1 sat for more than a year. Currently, Brutal Legend, Prince of Persia (2008), Ratchet and Clank: Crack in TIme, Saboteur, Just Cause 2, Okami, Darksiders, Sam N Max S1, and probably others, all sit about 90% complete.
 
What stops me?  Does it stop anyone else?

For some reason, I only do that with RPGs. Every other game I have to finish as soon as I can, but with RPGs, I get maybe half way, give up and then go back several years later, where I have to re-learn the battle system or whatever other system it has. It took me 5 years to finish FF9. I stopped playing Persona 4 when I stopped watching the Endurance run (around episode 40, I think) and I can't go back to either yet, I just...can't.

Do you buy new games often? If you do I suppose you're giving yourself a reason to be distracted from completing the game you were currently playing. If something gets too tough or seems a bit tedious you have the option to just start another game and then let history repeat itself I guess. I'm unsure really, that's just my theory on it! That and ofc rlf often gets in the way.

I only occasionally finish games completely. Sometimes I don't even finish the single player portions (I'm still trying to finish AC2, after kinda-beating it with a friend on his console). If I finish a game, I'm likely to finish it more than once. I always have a drive toward completionism, but to be honest I usually burn out on a game long before I get there. Usually it's RPGs that make me want to get everything. Strangely enough, though, the last few games I've played a lot (Dragon Age, Mass Effect 2, Red Dead Redemption) haven't tempted me at all to try to get 100% completion. I'm getting older, don't have as much time to play games, and have too many other things to do than spend 60+ hours for an achievement.

I'm a boss away from the end on P4, but mostly because I can't be bothered to grind up to ~85.
 
I have a similar issue, though it's even more focused, really. I tend to play games in one or two giant sprees and then never touch them again. I finished Heavy Rain 3 times or so, then took it out, packed it away, and have yet to return. I played Demon's Souls for about 20 hours before saying, "Fuck this!" and turning off my PS3. I even have my Gamefly FFXIII sitting in my PS3 right now, having not played it since about a week ago. I'm 40 hours into it or so and I'm constantly thinking, "Man, I should play that some more," but never get around to it.

Hmm, I've never thought about it much but I think I have a similar issue. I can easily play through half a game or more but I seldom finish them. 
 
Maybe you just don't want it to end? You want the game to last forever or something. I don't know, it's weird.

Sometimes, that could be a good thing too. What if the ending is a bad one? What if you don't want to know what it is, and just keep on playing?
 
Yes, I have a similar issue, in that I don't finish all of my games, but get pretty close to it. I stopped playing Super Mario Galaxy at 64 stars, because I lost my motivation to keep on playing. Princess Peach was rescued, Bowser lost, and good once again triumphed over evil. Not much more I really care to do.