The Myth of Sisyphus
Comments and mentions from HN threads:
Ask HN: Which non-technology book has influenced you the most and why?
MithrilTuxedo: Camus made life without specific reason or meaning acceptable.
Ask HN: Which books have made you introspect?
BreakfastB0b: ...if you find yourself worrying about existential nihilism then this is the book for you. I found it extremely useful after an intense psychedelic experience.