I've always been a completionist by nature, and when it comes to games I really don't play around (pun intended). I spend as long as it takes to completely finish a title, just as long as I'm super into it of course. Hell, even if it's not my favorite game I will at least play it through for an extended period of time to really see if it sucks or if I'm just being a sore loser and making excuses. On more than on occasion I've enjoyed certain titles that were deemed 'bad' just because I really gave them a chance. Add that mentality to being a pretty big trophy whore and you get a gamer who always has something to do and a game to conquer.
I feel like the best game experience is full of laughter, smiles, tears, defeat, and, of course, victory. It's pretty much the main motivator behind my completion missions. It's something that is hard to achieve through a minimal effort. Yes, it's hard. Yes, you're going to get pissed and lose sometimes. But when everything is done (especially in a lenghty JRPG with tons of formidable enemies and secret dungeons) there is just no greater sense of accomplishment for me than to know I won.
To all the users I've seen responding about not being able to finish their games, I urge you to preserver and see it through to the end. Before I got on my kick off beating everything I was in the same sized boat. I could never see my adventures all the way through without getting distracted or bored. I guess the biggest difference now is that I take whatever steps neccesary to get past the point of stuck. I'll use a guide for a quick reference, watch a youtube walkthrough for that specific point, draw maps if I'm lost. Anything really.
I guess for me it all helps up the immersion factor for any game when I conquer all that it has to offer. The way I see it, it's hard to appreciate a book if you don't read the entire story.