“Every man bears the whole form of the human condition.”Michel de Montaigne · Eseuri · 1580 · III, 2
Montaigne claims there is no such thing as a stranger: each of us contains the potential for every human experience, from glory to infamy. The mechanism is recognition: what we condemn in others exists in us as a possibility, so studying oneself becomes studying everyone. When you rage at a friend's betrayal, you can recall having lied yourself; the pride of not being "like him" is a comforting illusion.
Why it matters An antidote to hasty judgment of others and to the illusion that we are essentially different from those we criticize.