I saw (500) Days of Summer tonight. When I was young, I lived in my head, just like the young man in this movie. In the movie, he gets involved with a free spirit, which is pretty much something that happens a lot in the fantasies of young guys who live in their heads, not so much in real life.
In the movie, the guy has an interior life; the girl doesn't, which reinforces the fantasy aspect.
So I was really tripping emotionally while watching the movie.
For the record, as a young poet I was engaged for 24 hours to Jay Sheckley, who was Portland's Madonna at the time. Someone told me once the high point of her life was following Jay around San Francisco for eight hours.
After I started studying story structure (the ideas that became a story is a promise), I re-read the hundreds of short stories I'd written when young, and a few novels. Many were written with main characters who lived in their heads, generally a terrible choice for stories, since readers often want to experience a story through an active character on some kind of journey. Not with quiet guys who think a lot and don't do much.
Yes, it can be done, but it's easy to do badly, hard to do well.
Anyway, 500 Days makes its story more interesting by chopping up the narrative and manufacturing a happy ending.
For the record, I sweat bullets the whole 24 hours I was engaged to marry Jay. I really, really enjoy relating the experience more than I enjoyed living through it.