Mental Toughness — Become the forged version of yourself. The 40% Rule. The Accountability Mirror. The Cookie Jar. The Suck Index. The Box.

Mental toughness is not grit. It is not Stoicism. It is not Sisu. It overlaps with all three and is the same as none of them. The modern doctrine — codified by David Goggins, Jocko Willink, Mark Divine, and the SEAL selection programs they came out of — is built on a small set of testable claims: that the brain has a governor that shuts you down at around 40% of your true capacity, that the inner