Today, the justifications appear altogether less convincing. It usually has something to do with proving something to yourself and raising money for charity. I think the two should be separated: with regards the latter, just explain what it's for, and I'll consider searching behind the sofa; the former, on the other hand, is not behaviour I feel I should be seen to endorse. For running marathons is unbridled lunacy.
David Aaronovitch: Looking every part the mean and moody, yet amused in an existentialist sort of way, long-distance runner. May have lost his damn mind.
Update: Further confirmation of the connection between marathon-running and losing of the damn mind.