People often assume running a full-marathon is like running two half-marathons consecutively: 42.2 kilometres = 21.1 K + 21.1 K. It's not exactly how I look at a race. The problem with the equal split is that by the time I finish the first 21.2 K, my natural reaction will be: Now I have to do it all over again!
To me, 42.2 K = 32 K + 10.2 K
I usually run my first 32 K at my target pace. But for the last 10 K, exhaustion, cramps and all kinds of physical limitations will creep in. That's when the mental strength kicks in. An athlete with good mental training will be able to draw deep from his/her physically depleted "well" to find the necessary energy and will to go on. It is not easy, but it can be done. So far, I have managed to finish all my full- and half-marathon races without a DNF (did not finish).
Wellness = Physical health + Mental health
Strength = Physical strength + Mental strength