I know it is dangerously addictive because I’ve seen my brother, uncle, dad, and sisters-in-law slip towards full-time obsession as they strain to trim seconds off their personal bests. On Easter Saturday my brother dragged us to the Guildford run — he won and, in a not-that-pleasing symmetry, I was last, but the stewards were still smiling as my daughter, niece and I crossed the line more than 10 minutes after everyone else. It gets to you: a combination of humiliation, curiosity and vanity that makes you think that perhaps you ought to have another go.