David Goggins, US Navy Seal. I learnt about him last year but he never fails to inspire. He runs for kid's who's parents die out at war and raises money for them to go to college. He runs ultramarathons. He once even ran for 48 hours straight around a 1 mile track just to see how many miles he could get for charity. 48 hours, running, straight, no sleep.
This is universal, not just for training for the military. Just watch this, if you’re not interested 10 seconds in don’t watch the rest….trust me, this will motivate and guide you so much.