Many of the quotes that are most important to the novel are quotes that show how Mark Watney is able to assess a problem, control his fears, not give up or lose hope, and stay positive. Often, his positivity is closely linked with his sense of humor. In fact, readers are told that Watney's sense of humor is a factor in being chosen for the mission in the first place. The following quote conveys to readers many of Watney's character traits:

I'm going to be setting a fire. In the Hab. On purpose. If you asked every engineer at NASA what the worst scenario for the Hab was, they'd answer "fire."

The quote is important because it shows that Watney is well aware of the danger that he is in, and he is well aware of the fact that he is intentionally adding to the danger. What's important to note is that Watney is never cavalier about his dangerous decisions. He makes them with knowledge that is based on his training and advice from NASA. He's also consistently able to make a joke about the action that he is about to perform. As Watney notes in his diary,

NASA, however, is absolutely shitting itself . . . To them, equipment failure is terrifying. To me, it's "Tuesday."

Watney's situation on Mars is constantly shifting. He has a lot of problems before him, and he can't fix all of them at once. As soon as he fixes a particular problem, another problem rears its head. That's why Watney can be so nonchalant about equipment failure: it's happened so much that it's normal. Despite the facts—that Mars is out to kill him and his equipment is always on the verge of failing—Watney never loses focus on the task at hand. He knows that he needs a goal. He knows that without a goal, he has no hope. Additionally, Watney understands the importance of keeping his goals simple and achievable.

I don't have a plan for surviving four years on one year of food . . . For now, I'm well fed and have a purpose: Fix the damn radio.

A large part of the story of The Martian revolves around a conflict of man versus nature. Mars is a hostile environment, and any mistake Watney makes is likely going to be his last. Mars doesn't have a desire to kill Watney, but Mars will eventually kill him if given the chance. Despite Mars essentially being the story's antagonist, it is interesting that Watney develops a sort of kinship with the planet. At the end of the novel, he admits that it feels strange to be leaving.

I still can't quite believe that this is really it. I'm really leaving. This frigid desert has been my home for a year and a half.