The greatest thing in the world is to know how to belong to oneself.

[La plus grande chose du monde c’est de sçavoir estre à soy.]

Michel de Montaigne (1533-1592) French essayist

Essays, Book 1, ch. 38 (1.38), “Of Solitude [De la solitude]” (1572) [tr. Frame (1943), 1.39]
    (Source)

Present in the 1st (1580) edition.

Some translators use the 1588 sequence of chapters, not the 1595, and so identify this as ch. 39.

(Source (French)). Alternate translations:

The greatest thing of the world, is for a man to know how to be his owne.
[tr. Florio (1603)]

The greatest thing in the world is for a person to know that he is his own master.
[tr. Cotton (1686)]

The greatest thing in the world is for a man to know that he is his own.
[tr. Cotton/Hazlitt (1877)]

The greatest thing in the world is to know how to belong to oneself.
[tr. Ives (1925), 1.39]

The greatest thing in the world is to know how to be oneself.
[ed. Rat (1958), 1.39]

The greatest thing in the world is to know how to live to yourself
[tr. Screech (1987)]

The greatest thing in the world is to know how to belong to oneself.
[tr. Atkinson/Sices (2012)]