I love the vagueness of 'don't pick at it'. Presumably 'it' being the scab on your knee, the loose thread on the arm of the sofa, that bit of peeling paint in your bedroom, the inside of your left nostril, the blister on your heel, the label on the HP sauce bottle, the cat's mangey leg, etc etc. Kind of sums up childhood. Not that I ever really learned to stop.
Well said, C - the remark was always regarding scabs, though. I had one on my knee for about a year because I couldn't resist the perverse pleasure of breaking it open again.