Plato Quotes
What the expression is intended to mean, I think, is that there is a better and a worse element in the character of each individual, and that when the naturally better element controls the worse then the man is said to be "master of himself", as a term of praise. But when - as a result of bad upbringing or bad company one s better element is overpowered by the numerical superiority of one s worse impulses, then one is criticized for not being master of oneself and for lack of self control.
Plato. The Republic. Translated by Desmond Lee, Penguin Books, 1974, p. 203.
Plato (/ˈpleɪtoʊ/ PLAY-toe; Greek: Πλάτων Plátōn, pronounced [plá.tɔːn] in Classical Attic; 428/427 or 424/423 – 348/347 BC) was an Athenian philosopher during the Classical period in Ancient Greece, founder of the Platonist school of thought and the Academy, the first institution of higher learning in the Western world.