The most difficult thing for me in writing a novel is creating backgrounds for my characters. I believe our personalities stem from not only what frame of mind our moms were in while carrying us, but also our environment and how we're raised. So why are my characters the way they are? What motivates them? Are their actions and reactions logical, in sinc with their personalities?
In Techniques of the Selling Writer by Dwight V. Swain, we read:
"Your ideas about why a man takes a certain path can quite possibly prove as valid as another's. In characterization, as in anything else, you have to act on the courage of your convictions. If you intrigue your reader with your concepts, he'll go along."
"A 'living' character is not necessarily 'true to life,'" declares poet-dramatist T.S. Eliot. "It is a person whom we can see and hear, whether he be true or false to human nature as we know it. What the creator of character needs is not so much knowledge of motives as keen sensibility; the dramatist need not understand people; but he must be exceptionally aware of them."
So. . . I guess anything goes. . .as long as it works.