A person can go on living fairly well, seem to be a human being, be occupied with temporal matters, marry, have children, be honored and esteemed — and it may not be detected that in a deeper sense this person lacks a self. Such things do not create much of a stir in the world, for a self is the last thing the world cares about and the most dangerous thing of all for a person to show signs of having. The greatest hazard of all, losing one’s self, can occur very quietly in the world, as if it were nothing at all. No other loss can occur so quietly; any other loss — an arm, a leg, five dollars, a wife, etc. — is sure to be noticed.

Søren Kierkegaard (1813-1855) Danish philosopher, theologian
The Sickness unto Death, “The Forms of This Sickness, i.e., of Despair,” 1.a.1 (1849)

Alt. trans.:
• "A man may nevertheless be perfectly well able to live on, to be a mn, a it seems, to occupy himself with temporal things, get married, beget children, win honor and esteem -- and perhaps no one notices that in a deeper sense he lacks a self. About such a thing as that not much fuss made in the world for a self is the thing the world is least apt to inquire about, and the thing of all things the most dangerous for a man to let people notice that he has it. The greatest danger, that of losing one's own self, may pass off as quietly as if it were nothing; every other loss, that of an arm, a leg, five dollars, a wife, etc., is sure to be noticed." (Source)
• "But to become fantastic in this way, and therefore be in despair, although usually obvious, does not mean that a person may not continue living a fairly good life, to all appearances be someone, employed with temporal matters, get married, beget children, be honored and esteemed -- and one may fail to notice that in a deeper sense he lacks a self. Such things cause little stir in the world; for in the world a self is what one least asks after, and the thing it is the most dangerous of all to show signs of having. The biggest danger, that of losing oneself, can pass off in the world as quietly as if it were nothing; every other loss, an arm, a leg, five dollars, a wife, etc. is bound to be noticed." (Source)