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. (2.21)
Sometimes, you just need take things one at a time. If Mark were to spend too much time worrying about how to get out of this mess, he'd lose focus on short-term survival. Plus, setting goals will help his morale—without them, he'd probably feel lost.
Sirius 1 was aborted after one hour. I guess you could call it a "failure," but I prefer the term "learning experience." (7.68)
This sounds straight off a motivational poster, likely featuring a prominent photo of a cat. Not that we're complaining. With crazy stuff happening on a daily basis, Mark can't expect things to go perfect the first time around. The key will be working harder the second time.
So I cheated. I upped my O2 mixture. It really helped a lot. Probably shouldn't make that a habit. (9.88)
Careful now, buddy. This is the first time that we see a downside to Mark's never-say-die mentality. Everyone has their physical and mental limit, and Mark would be wise to not overstep his own.
Before I was in contact with NASA, I would have worked more than eight hours. [...] But NASA's got a lot of nervous Nellies who don't want me out longer than spec. (17.71)
Careful now, bro. A few days later, Mark proves NASA's point by straining his back lugging rocks around, which puts him out of commission for a solid week. Mark is so close to the finish line that it would be downright silly to screw things up now. Perseverance is important, but that doesn't mean you shouldn't use your head.
My guess is pockets of ice formed around some of the bacteria [...] Life is amazingly tenacious. They don't want to die any more than I do. (17.89)
Mark's will to survive is hardwired into his DNA. He's operating off pure instinct, doing the same thing that any living creature would do in his situation. Of course, he has the benefit of modern technology and his handy spacesuits, so at least he has a leg up on the competition.
"My people have especially commented on the work ethic of your man, Mitch Henderson. He is very dedicated." "He's a pain in the ass," Teddy said. (19.59-60)
Mitch is the single most tenacious individual we come across in The Martian. This attitude makes him a lot of enemies: after all, no one likes to be called out on a daily basis. What no one can dispute, however, is his fire. He won't let anything get in the way of achieving his mission—even his coworkers' feelings.
"If the probe can't attach top the docking port for some reason, Beck will open the probe and carry its contents to the airlock." (19.124)
That actually sounds pretty fun. Still, it also sounds really dangerous, and we admire Beck for agreeing to do it. The dude is willing to jump out of a moving spaceship just so he can rescue his friend. At this point, it's clear that the Hermes crew won't stop fighting.
"It's amazing how much red tape gets cut when everyone's rooting for one man to survive." (21.18)
Isn't that the truth. As a government organization, NASA isn't exactly known for doing things quickly. This whole operation wouldn't have been possible without the hard work of people like Mitch, Mindy, and Rich Purnell. Everyone played their part.
"There's always hope," Venkat said. [...] "Mark Watney is now an expert at surviving on Mars. If anyone can do it, it's him." (22.25)
After everything is said and done, Venkat—and NASA as a whole—has gained a lot of respect for Mark Watney. Mark is stuck in an impossible situation and has fought through it out of sheer force of will. Sure, his scientific background and training comes in useful, but the most important contributor to his survival is his sheer willpower.
"I'm, not talking about faith in God, I'm talking about faith in Mark Watney." (22.72)
Mark began this tale as a humble botanist: a supremely normal dude. Yet, by the end, he becomes the kind of guy you have faith in no matter what. If that's not a testament to the guy's determination, then we don't know what is.