Very touching

A true story;
One day, a son asks his dad "Daddy, would you like to run a marathon with
me?". The father says "yes".
And they run their first marathon together.
Another time, the son asks his dad again "Daddy, would you like to run a
marathon with me?". The father says "yes son".
One day, the son asks his father " Daddy, would you run the Ironman with
me?"
The Ironman is the most difficult triathlon ever ( 4 kms swimming, 180 kms
bikin, 42 km running )
And the dad says "yes".
The story looks simple until you watch the following clip.

http://www.youtube.com/watch?v=VJMbk9dtpdY