“It's necessary to have wished for death in order to know how good it is to live.”

Ibid., p. 276
The Book of Disquiet
Original: Saber não ter ilusões é absolutamente necessário para se poder ter sonhos.

Source: The Prince (1513), Ch. 15; translated by W. K. Marriot

In a letter to Charles Babbage, as quoted in The Shadow of the Telescope: A Biography of John Herschel by Günther Buttmann, p. 14

Source: Atlas Shrugged

Fire from Heaven (1969)

Confessions of a Revolutionary (1849)
Context: It is necessary to have lived in this insulator which is called the national assembly, in order to perceive how the men who are the most completely ignorant of the state of the country are almost always the ones who represent it. I set myself to read everything that the distribution bureau sends the representatives: proposals, reports, brochures, even the Moniteur and the Bulletin of the laws. The greater part of my colleagues of the left and the extreme left were in the same perplexity of spirit, in the same ignorance of the daily facts. The national workshops were spoken of only with a kind of fright; for fear of the people is the defect of all those who belong to authority; the people, as concerns power, is the enemy.

Statement to Captain William Hull prior to his spying mission, as quoted in "Captain Nathan Hale (1755 - 1776)" http://www.connecticutsar.org/patriots/hale_nathan.htm by Rev. Edward Everett Hale
Context: I wish to be useful, and every kind of service necessary to the public good becomes honorable by being necessary. If the exigencies of my country demand a peculiar service, its claim to perform that service are imperious.

Post-Presidency, Nobel lecture (2002)
Source: The Nobel Peace Prize Lecture

Source: Life, the Truth, and Being Free (2010), p. 61