“When it just doesn’t make any logical sense to go on, that’s when you use your emotion, your anger, your frustration, your fear, to push further, to push you to say one thing: I don’t stop. When your feelings are screaming that you have had enough, when you think you are going to break emotionally, override that emotion with concrete logic and willpower that says one thing: I don’t stop. Fight weak emotions with the power of logic; fight the weakness of logic with the power of emotion.”
Jocko Willink, Discipline Equals Freedom (Page 23)