I worried that I didn't sit down and plan out my characters in detail, filling out elaborate character sketches that other seemed to. Like my story, I have a solid concept of the characters in my head but if I force myself to think about them, nothing comes to mind or they end up being cardboard. As I write the story, they come to life for me and I let them unfold naturally. I don't know how common this is since I keep reading about people who do character profiles before they start writing.
Recently, I read a blog by a writer who also doesn't do character sketches but discovers her characters as the story goes (and do you think I can find this blog again? Nope.). I was happy that I wasn't the only one.
As I write both the story and the characters reveal themselves and I go with it. Sometimes I think I know my character then he/she does or says something I hadn't expected. It can be quite interesting. My husband thought I was crazy until he saw an interview with actor John Cleese, who said that sometimes the character takes over during acting and that he had heard that it happens with some writers too. After that, my husband believed me.
During my first novel, I had a hard time developing the main character's love interest, mostly because I was forcing his personality. Once I stopped and listened to him, his true character revealed itself and he was a deeper and more rounded character. My great epiphany about him came while I was working out and I allowed my mind to wander.
The down side is that either you need to stop writing and make notes about your character(s) as you go or have a really good memory about details you have written. I do both, depending on how my writing session is going. Sometimes, when I'm doing a read through, I'll keep a pen and paper handy to make character notes as I read.
So, for anyone else who has trouble plotting out characters in detail before writing, you're not alone. I fine tune my characters and story though multiple revisions, like any writer. As long as you have a good concept before you start, there's nothing wrong with letting characters write themselves if that's what works for you.