We often struggle to create realistic characters; they don’t always seem believable. We can usually recognize characters that feel two-dimensional, but we don’t always know why. I’d like to submit that one of the primary reasons we have trouble with characterization is we rarely ask ourselves how our characters got where they are.
With very few exceptions, all characters had a childhood. What did your character want to be when they grew up? The success or failure of that dream is a crucial part of the journey that brought your characters to their place in your story.