There is no limit to the size of our dreams and no known frontier to human ambition. For some this is a bumper sticker and for others a prayer to live by. This year a 72-year-old carpenter rowed across the Atlantic in a boat built in his garden. Two years ago, Xia Boyu, then 69, summited Everest, the same mountain which claimed his feet through frostbite in 1975.

There are those who wish to travel to Lourdes and those who take their faith to different shrines. Xia kept returning to Everest, as if the mountain beckoned him. It represented a "personal challenge" and it is a beautifully elastic phrase. Among runners, for instance, your personal challenge may be to run to the next bus stop or to one day finish a marathon.