An old philosophical friend of mine was grown, from experience, very cautious in this particular, and carefully avoided any intimacy with [captious, overcritical] people. He had, like other philosophers, a thermometer to show him the heat of the weather, and a barometer to mark when it was likely to prove good or bad; but there being no instrument invented to discover, at first sight, this unpleasing disposition in a person, he, for that purpose, made use of his legs; one of which was remarkably handsome, the other, by some accident, crooked and deformed. If a stranger, at first interview, regarded his ugly leg more than his handsome one, he doubted him — if he spoke of it, and took no notice of the handsome leg, that was sufficient to determine my philosopher to have no farther acquaintance with him. Every body has not this two-legged instrument; but every one, with a little attention, may observe signs of that carping, fault-finding disposition, and take the same resolution of avoiding the acquaintance of those infected with it. I therefore advise those critical, querulous, discontented, unhappy people — if they wish to be respected and beloved by others, and happy in themselves, they should leave off looking at the ugly leg.
— Benjamin Franklin, 1780