Characters have their own minds. They have growing pains and awkward phases. You're most likely at one point going to be unhappy with them and how they've turned out, but that isn't always a bad thing or inherently means the character needs to be scrapped.
Don't worry about defining their weaknesses, strengths, goals, ambitions, etc right away. Don't worry if it's too vague or shallow right now. Just write or draw or fantasize. It'll come eventually. They aren't real but you're still getting to know a person (or whatever species they may be-- you're getting to know someone), and you're not gonna know everything about them right away.
You don't have to wait until they're clear cut and chipped at until they're as detailed as a Michelangelo sculpture to begin creating the story. There's characters I've haphazardly thrown into a story within an hour of creating them and some of them are some of my most important and fleshed out characters now that brought a clearer direction to my stories.
