A "simple" character (particularly a servant or rural character) displays uncommon wisdom — usually much to the surprise of an arrogant main character. Creates An Aesop moment.
This would seem to derive from Cervantes' Don Quixote, where the archetypically "simple" Sancho Panza occasionally produces statements of great wisdom (although in that case the main character, Don Quixote, often fails to notice or credit that wisdom).
Dungeons & Dragons players will lecture, in great detail, that Wisdom and Intelligence are not the same thing: while a character with high Intelligence would be able to identify a Cursed Item as such, a character with high Wisdom would know better than to touch it.
Compare Dumbass Has a Point, which is what said Insufferable Genius may say after hearing the simple character's idea, and Eccentric Mentor, when the character is not simple, but just extremely quirky.
See also: Achievements in Ignorance, Too Dumb to Fool, Whoopi Epiphany Speech, Infallible Babble, Hanlon's Razor, Profound by Pop Song, and Wisdom from the Gutter. Contrast Ditzy Genius, which is in many ways the diametric opposite of this trope, and Seemingly Profound Fool, in which other characters erroneously read wisdom into the genuinely banal observations of a bona fide fool.
