Michel Duval is the psychiatrist for Mars's first one hundred colonists, and while on Mars, he undergoes a bit of a personal trauma. Luckily, his clients are literally millions of miles away from another psychiatrist, so his practice doesn't suffer from his neglect.
The simple fact is that Michel is homesick. He hates the look and feel of Mars, claiming it's too cold and that the landscape looks like "[w]allpaper in hell" (4.2.39). The disconnect he feels from the world surrounding him branches off into his relationship with the other First Hundred. He believes he exists not as a true human being with relationships but as a "program" (4.2.65). In other words, he simply acts and speaks as he feels others expect him to.
At the end of Part 4, he runs away with Hiroko and her groupies to start a new Mars settlement out in the rock-strewn wilderness. And he returns late in the novel to save Ann, Sax, Simon, Nadia, Frank, and Maya from UN forces. When he does, his demeanor suggests he's improved significantly, but the real tell is how he drives through the Martian canyons. A stranger to the planet no longer, he deftly navigates the other Firsts through the perils en route to Hiroko's refuge.
No joke, you can tell a lot about a person by how they cruise—and in the end, Michel's cruising with confidence.