In this essay, Anne Lamott writes about characters. One thing she said really struck me. I can't quote it exactly but it's sort of like this. Every story needs a character that resonates with the reader. I have favorite writers. I'm sure everyone does. Thses authors I read just about everything they write but sometimes I can't read one of their books. The above bit was the reason why for me. The character didn't draw me into the story.
Another thing I found interesting and true is that every character has part of yourself. Has to be. How else can the emotions you want to express be shown to the reader. Characters are composite and they take in the good and the bad of nature. You can't learn and understand a character until you've spent time with them and also allowed them to surprise you.
It's the surprise moment that really zings. The character becomes a friend and develops all those rounded sides.
So how much of your character belongs to you and how much to observation, other people and even nebulous qualities. Taking a character through a story is one way to learn