I am just curious - what is it that you do to challenge yourself everyday? Wake up early to train? Get hot / Get cold / Get uncomfortable? Diet / Fast? Set goals? Do tough endurance events? 

Remember there is a fine line between mental toughness and stupidity - what do you think that line is? For me it is pushing into injury - now you cannot train anymore.  But in life or death situations there is doing whatever to get out alive. So that line is moveable depending on the situation...