There is this story that I was working on, for an extended period of time. I have scrapped many ideas and drafts but I just could not seem to let go. The idea of this story, in my mind, is simply too precious for me to abandon. This is a story heavily driven by character and character development, but I just don't know how to portray him.
Like the title suggests, the protagonist William is a broken man, he is defeated, in both body and mind, and has lost his drive because of severe trauma. Now he is alone, living off past savings and has no will to do anything. In short, he does not know his reason to live. He sees growth, interactions and social advancement as pointless, and spends most of his time either asleep, or drunk. This is a character that has no more reason to live, but sees no rationale to die. And he will continue "living" this way if not for a convenient plot device showing up and asking him for help.
In addition to the above, William is also mentally ill, severe PTSD aside, he is also prone to Delirium and Schizophrenia. This made him question reality and his purpose of existence, but reaching no answers. He also doubts the existence of love, happiness and other generally positive emotions, often citing them as "a convenient lie". He is also incredibly conflicted due to this, as he contemplates his own death frequently, but never proceeds to do so when this idea "might not be his own".
He is, needless to say, extremely cautious and paranoid. After all, what can be trusted when he cannot trust his own mind? However, this is not in the way of "everyone will take advantage of me" paranoia. "After all, what more can be taken from me?" He just continues to question everything that was told, but with no answer in sight. If life be nothing more than an endless series of questions with no answer, why try anything at all?
My question is: given such a character as this, is character development even possible? How do I even begin the plot when William outright refuses to cooperate? What could possibly drive a character such as this? I refuse to simply handwave this problem away and say he helps because reasons, I want this story to feel real, and I want readers to empathize with William's feelings (or lack thereof), his illness, and most important of all, the humanity that he (somehow) regains. My problem is that I have absolutely no idea how to do this, so any help from you will be appreciated.
Additional points to consider: The world in the story is very similar, if not outright identical to ours. Miracles does not exist, so that will not be a factor that he looks forward to.
I mentioned he is "once brilliant" as a military scientist, he will not ever regain that level of intellect. I want him to venture as a human. He will not offer help in the hopes regaining his mind.
He knows perfectly well that he is not some center of the world type person. This world does not revolve around him, and he has no superhuman influence within this world. In fact, this is the argument he gave for not helping at first.
That is all from me for now, leave any questions and suggestions in the comments. Feel free to edit this post to make it better.
Summary for the lazy: Given William's character above, what could possibly drive him to leave isolation and venture to help others? What would possibly cause this character to change and develop? And in the case that he really does change, what would theses changes be?