A Parable on Optimism, by Benjamin Franklin
An old philosophical friend of mine carefully avoided any intimacy with pessimistic people. He had a thermometer to show him the heat to mark when the weather was likely to prove good or bad, but there being no instrument invented to discover at first sight this unpleasing disposition in a person, that of being a pessimist, he for that purpose made use of his legs, one of which was remarkably handsome, the other, by some accident, was crooked and deformed.
If a stranger at the 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 and have no further acquaintance with him.
Everybody has not this two legged instrument, but everyone 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 that if they wish to be respected and beloved by others, and happy in themselves, they should leave off looking at the ugly leg.