The Martian is an outlier in its success, but it's far from the only instance of successful self-published sci-fi. Recent examples I've read include The Powers of Earth[1] by Travis Corcoran and Theft of Fire by Devon Eriksen. In both cases, the authors quit their day jobs (I think both worked in software) and are now full time writers.

1. https://en.wikipedia.org/wiki/The_Powers_of_the_Earth