FRIENDSHIP. A mutual belief in the same fallacies, mountebanks, hobgoblins and imbecilities.

H. L. Mencken (1880-1956) American writer and journalist [Henry Lewis Mencken]

A Book of Burlesques, “The Jazz Webster” (1924)
    (Source)

Variant:

Friendship is a common belief in the same fallacies, mountebanks and hobgoblins.
[Chrestomathy, ch. 30 "Sententiae" (1949)]