I would say what hurts the most is letting someone important to me down. Although I'm getting better at not caring as much.
My biggest fear is being out of control. Like in Robb's near drowning incident.
Facing something unknown scares me and I'm worried I may not be able to handle it. I'm also getting better at this one, realizing I have handled everything else so far, so I'll probably be just fine.
I haven't figured out how to write either of these into my project just yet. Thinking about this... and open to ideas.