"Self-control is the chief element in self-respect, and self-respect is the chief element in courage." - Thucydides.
"The enemy is within the gates; it is with our own luxury, our own folly, our own criminality that we have to contend." - Cicero.
"Self-reverence, self-knowledge, self-control–these three alone lead life to sovereign power." - Alfred Tennyson.
"I count him braver who overcomes his desires than him who conquers his enemies; for the hardest victory is over self." - Aristotle
"The first and best victory is to conquer self. To be conquered by self is, of all things, the most shameful and objectionable." - Plato.
"We improve ourselves by victories over ourselves. There must be contest, and we must win." - Edward Gibbon.