Quote 7
I wonder if they'll ever find out what really happened. I've been so busy staying alive I never thought of what this must be like for my parents. (2.63)
The worst part about this ordeal is that no one even realizes that Mark is alive. If they did, he might be a bit more optimistic about his chances. Instead, he sees no way out and loses hope immediately. Fortunately, this fear-induced funk doesn't last long.
Quote 8
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." (4.14-15)
Desperate times call for desperate measures. This passage shows how well Mark is able to handle his fear: instead of allowing it to drive his actions, he acknowledges it and moves forward. He could've easily just curled up in a ball and binge-ate his ration packs, but Mark Watney isn't going down without a fight.
Quote 9
There's probably symbolism there. Phobos is the god of fear and I'm letting it be my guide. Not a good sign. (9.26)
Well, Mark summed it up better than we ever could. Frankly, he usually screws thing up when he lets his fear take control and prevent him from making wise decisions. At least the guy's aware of it now.