Who said "One must impose discipline on oneself."?

This quote is attributed to The King.

One must impose discipline on oneself. - The King

"One must impose discipline on oneself."

The King

Character in The Little Prince

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"It is a matter of discipline"

"I am who I am and I do what I do."

"One must require from each what each can perform."

"One must demand that a king be dignified."