This is a really good post, sometimes I find that I have to re-affirm these kinds of points and make a concious effort not to forget them.
I think another thing that is important is consequences for actions, for example. Using the idea of the character who wants to not be in pain, in their quest for painlessness, maybe they take pain killers. Which, they get addicted too, after there pain is gone, then their addiction manifests in a pain, that keeps them taking the pain killers.
Or maybe, the character who wants painlessness dies at the end. Their final thought could be. It's warm and cold. There's no happy or sad, it's just peaceful. No pain or worries. Then everything goes dark. - It's like they got what they were looking for, but it wasn't how they expected it.
I remember my scriptwriting tutor always said that, try and wrap things up at the end of a script by giving the character what they wanted, but, maybe not how the expected. Unless it's a certain genre of film.
It's so interesting, I think flaws for characters is really important too. I love nothing more than someone who's hopeless, but, especially if they don't even realise that they have a flaw.