Mark Watney is a hilarious character. His sense of humor is actually one of the reasons that he was chosen for this particular mission to Mars. Watney is an incredibly intelligent man, and his knowledge and skills as a botanist are also a reason for his selection, but his ability to keep fellow crewmates in good spirits is highlighted as a reason for why he was chosen over other more qualified scientists.
"He sounds like a great guy," Cathy said.
"He really is," Irene said. "He was chosen for the mission in part because of his personality. An Ares crew has to spend 13 months together. Social compatibility is key. Mark not only fits well in any social group, he's a catalyst to make the group work better."
When things get tough, Watney cracks more jokes. Consequently, readers hardly ever get to see Watney's emotional state. He stays goal-orientated and task-focused, and he only gives readers enough information about his past to show us how it applies to the current problem. This is how we find out that Watney grew up in Chicago, Illinois. He mentions that he attended the University of Chicago multiple times, but that doesn't necessarily mean he grew up in Chicago.
In "Sol 119," Watney confirms that he grew up in Chicago. He is telling us about the need to clean the solar cells, and Watney states that it reminded him of growing up in Chicago and having to shovel snow. In "Sol 209," Watney again mentions growing up in Chicago when he explains that waking up in a freezing cold environment was "nostalgic" for him.
Cold night last night. The solar cells were still detached from the farm, so I had to leave the Hab in low-power mode. I did turn the heat back on (I'm not insane), but I set the internal temperature to 1C to conserve power. Waking up to frigid weather was surprisingly nostalgic. I grew up in Chicago, after all.