Bring to mind, please, a tree which you have admired: a tall tree – a monarch of the forest, perhaps. There it stands, a magnificent specimen, towering against the sky.
Now, if you please, imagine that you must climb that tree to the very top, with a 60-pound pack on your back. As soon as you reach the top, you must leave your burden and descend, only to start up all over again with a fresh load. Furthermore, you must climb this tree 12 times during the day. And you must make a similar number of trips up the tree every day in the future.