The 40% Rule................................

    The human body is like a stock car.  We may look different on the outside, but under the hood we all have huge reservoirs of potential and a governor impeding us from reaching our maximum velocity.  In a car, the governor limits the flow of fuel and air so it doesn't burn too hot, which places a ceiling on performance.  It's a hardware issue;  the governor can easily be removed, and if you disable yours, watch your car rocket beyond 130 mph.
     It's a subtler process in the human animal.
     Our governor is buried deep in our minds, intertwined with our very identity.  It knows what and who we love and hate; it's read our whole life story and forms the way we see ourselves and how we'd like to be seen.  It's the software that delivers personalized feedback—in the form of pain and exhaustion, but also fear and insecurity, and it uses all of that to encourage us to stop before we risk it all.  But here's the thing, it doesn't have absolute control.  Unlike the governor in an engine, ours can't stop us unless we buy into its bullshit and agree to quit.
     Sadly, most of us give up when we've only given around 40% of our maximum effort.  Even when we feel like we've reached our absolute limit, we still have 60% more to give!  That's the governor in action!  Once you know that to be true, it's simply a matter of stretching your pain tolerance, letting go of your identity and your self-limiting stories, so you can get up to 60%, then 80% and beyond without giving up.  I call this The 40% Rule, and the reason it's so powerful is that if you follow it, it will unlock your mind to new levels of performance and excellence in sports and in life, and your rewards will run far deeper than material success.

-David Goggins,  Can't Hurt Me:  Master Your Mind and Defy The Odds