There is a difference between wishful thinking and motivation enough to actualize. I agree that one will most likely not roll out of bed and complete a marathon, but do not underestimate the power of belief. If one believes strongly enough, I have no doubt that the human body unencumbered by obesity can complete an ironman with no training. It turns out that fostering and synthesizing such strength of belief requires either a lifetime of devotion to meditation, the usual physical training athletes do (many mental journeys happen in this process as well), or fantastic cosmic circumstance.