I sometimes cast an eye along the student bike sheds at work. One time, I saw an MTB with the front v-brake disconnected. All the parts seemed visually fine. Funny, I thought, why would someone disconnect a perfectly good front brake? Oh, I see, the wheel is way out of true, must have been rubbing too much to ride . . . wonder what's up with the wheel - I pick up bike and give the wheel a spin, true as a laser beam, momentary bafflement, something weird happened with the hub? Oh, no! Look! one wheel nut has come loose and the axle has jammed halfway down the drop-out. Find spanner, fix, reconnect brake, find student, have fatherly talk about bike maintenance, mechanical sympathy and the art of staying alive . . .