...through general hamfistedness?
Wheel bearing change: It was all going so well at about 10pm last night, about to finish and feel all satisfied at a job well done - then I uttered those immortal words 'this has all been too easy'.
I managed to put the axle end-caps of my rear ProII on the wrong sides, probably through rushing. Then spent some time trying to hammer the bejesus out of them, convinced that the bearings had somehow become unseated, only to realise my mistake eventually. Not before (what a surprise!), I had deformed said end-caps, so that they now wouldn't fit in the frame. I then spent some time filing them back into shape. Only to fit the wheel and find that it wobbles. The new bearings had collapsed, due to me hammering the crap out of them.
I. Will. Learn. One. Day.