You can endure a staggering amount of punishment.
Benefit(s): Whenever you gain 1 hit point as a fighter favored class benefit, you gain an additional hit point. Treat your effective Constitution score as being 4 higher for the purpose of determining when you would die from hit point damage. These benefits are retroactive.
Pathfinder Roleplaying Game Adventurer’s Guide © 2017, Paizo Inc.; Authors: Benjamin Bruck, John Compton, Crystal Frasier, Tim Hitchcock, Jenny Jarzabski, Isabelle Lee, Joe Pasini, Jessica Price, David Schwartz, and Josh Vogt.