Man may have the most excellent judgment in all other matters, and yet go wrong in those which concern himself; because here the will comes in and deranges the intellect at once. Therefore let a man take counsel of a friend. A doctor can cure everyone but himself; if he falls ill, he sends for a colleague.

Studies in pessimism. A series of essays... Selected and translated by T. Bailey Saunders... Third edition (ed. 1892)