okay, so pardon my slight copy/paste, BUT he's a former fighter pilot/boy genius who wasn't accepted by any crew after a traumatic brain injury, but he's still the best pilot in the galaxy (according to himself, he's still got a bit of an ego on him for having so many repeat rejections). tl;dr, his natural brain and his cybernetic brain don't always get along so he literally shuts down and freezes whenever he's overstimulated. sometimes if you ask him a complicated math or science question he'll just turn into a statue and then two hours later, after it's too late, he'll finally work it out and have an answer. think of him as a walking blue screen of death. so if he's the cranky doctor, i imagine charlie'll come to him a lot, like FIX MY BRAIN DOC but no can do, he's not fixable as far as we know. but if your guy is the sort to poke and prod and try to figure things out, charlie doesn't mind being poked and prodded in the name of science, and honestly when he freezes up, he can't complain about it, anyhow.