His doubts started with his changing values. Take a look at the things he holds most dear. The opinions, the causes, the risks and the opportunities. He noticed they were not as permanent or as important as he once thought. He found out they are interchangeable. Take out one strongly held belief and swap it, like a battery or a computer chip, for the complete opposite belief. Life goes on.
In fact he is becoming convinced that he is a programmable robot, more than an organic, free, human being. He looks down at his own arms. Is there blood under this skin? Is there a mechanical, robot-arm like Arnie in the Terminator movies? And blood doesn’t count as proof of life. What is “blood” anyways? Liquid full of little micro-robots delivering chemical loads and hormones around his body to keep the robot system in balance.
What would a robot do?