Ferriss has long had an obsession with Stoicism, the school of ancient Greek philosophy that was also adopted by Roman thinkers.
The most famous work of Stoicism may be the philosopher king Marcus Aurelius' "Meditations," of which Ferriss is a fan, but he's especially taken with Seneca's letters to his student Lucilious. The collection is, as Ferriss said, "about everything imaginable, and it's as applicable today as it was 2,000 years ago."
"Stoicism as a whole I think is the optimal operating system for thriving in high stress environments," he said.