A couple of weeks ago I decided to restart my current WIP after getting four chapters into my first draft. Despite following my outline and keeping with my proposed character development, there was a major flaw growing in the storytelling which I did not want in my story. One of my characters was in danger of developing a mindset akin to Stockholm Syndrome, but that does not match up with who and what he is. So I started over and added a new character who would help alleviate this flaw.
One of the things that I've found helps me in my editing (particularly dialogue) is when I assign a specific voice to my characters. This may be a celebrity or a person I know from life, but no matter where the voice comes from, it's always distinctive to me. Someone I've heard talk a lot. Someone who I've seen and heard express a wide range of emotions.