You spend an awful lot of time with people when you're writing.
Not real people. They get in the way. Unreal people. Imagined people.
And not all of them are the cheerful, supportive, well-balanced type.
That's not so hard when you're writing a downright evil villain who, although they must have hidden depths and some kind of comprehensible motivation, is a blackguard and a scoundrel. They are quite fun to write, although you might not invite them over for a cup of tea.
That's why we all secretly admit to loving characters like Deadwood's wicked Al Swearengen more than dour Seth Bullock, even though we know we should really be on the side of the sheriff and not the brothel-owning murderer and his fabulously Jacobean swearing.
But what about your favourite characters, the people you spend months exploring and expanding? What about their weak moments, their shameful days, the incidents that might crop up later on facebook or the tabloids or a seventeenth century police report? How do you write your hero or heroine into a corner from which they can never escape, into a pitiable state, into an embarrassing scene from which nobody emerges with honour?
And how can you not?