How does the author choosing mark watney as the narrator fit the content, mood, or style of the book?

Watney is trained as a scientist and engineer, and he approaches problems on Mars with an orderly, rational mindset. He breaks big problems down into smaller ones, as a way of making sense of them, and he doesn't allow himself to get too worried about theoretical. Instead, he exists in the world of facts: how many calories will he need? How much power does the rover require? Watney's scientific thinking can, at times, seem almost implausible; after all, he must contend with the enormous psychological strain of isolation on Mars (see theme 1). But Watney also knows that no amount of magical or superstitious thinking will get him home. Rather, he must look to his own trove of scientific knowledge, and NASA's guidance, to make his way to Schiaparelli and, eventually, to the Hermes.