Not too long ago, I read a book that made me really sympathetic for the main character. His outlook on life was depressing, he had lost sight of his goals, and he was even ruining relationships by not being honest (because to him, the confrontation just wasn't worth it). As the book progressed, I wanted to grab the guy, pull him aside, and tell him I'd be his best friend. That I'd help get his crap together. I was completely engrossed in the story, and by the time the ending came along, I was ready for closure.
And yet... I didn't get it. In fact, I wanted to chuck the book across the room when I finished, because it was as though my emotions had been strung along and I was at the top of the roller coaster and the author just walked off, leaving me hanging there staring down at the inevitable drop never to come.
Is that life? The imperfect ending? Sure, a lot of times it is. But, it's like Ms. Lamott's quote above. Tell me the story of how your character faced the situation, what they felt, and how it made them a different person (for better or for worse). There can be sadness and loss and the frustration of not having things "all together", yes; but at the end, give me closure, not a bunch of tears and an uneasy feeling making me wish I'd never picked up the book.