One day a son says to his father: Dad do you want to run a marathon with me?
The dad says yes and they run their first marathon together.
One day a son says to his father: Dad do you want to run the ironman with me?
The ironman is the most difficult marathon there is 4km of swimming, 180 km of cycling and 42 km of running.
The dad says yes and the do the ironman together.
Seems like a pretty simple story, until you see this video.