people don't know themselves as well as they know others; a fortune teller can't tell their own future
Proverb meaning that one is often blind to one's own affairs while being able to see others' clearly. The literal reading refers to an onmyōji (yin-yang master) who cannot divine their own fate.
As the proverb goes, 'even an onmyōji doesn't know their own fate'—we often understand others well but not ourselves.
A traditional Japanese proverb. The exact origin is uncertain, but it plays on the irony that a master of divination (onmyōji) cannot foresee their own future.