“A man is great by deeds, not by birth.”

Man's Greatest Achievement (1908; 1930)
Context: According to an adopted theory, every ponderable atom is differentiated from a tenuous fluid, filling all space merely by spinning motion, as a whirl of water in a calm lake. By being set in movement this fluid, the ether, becomes gross matter. Its movement arrested, the primary substance reverts to its normal state. It appears, then, possible for man through harnessed energy of the medium and suitable agencies for starting and stopping ether whirls to cause matter to form and disappear. At his command, almost without effort on his part, old worlds would vanish and new ones would spring into being. He could alter the size of this planet, control its seasons, adjust its distance from the sun, guide it on its eternal journey along any path he might choose, through the depths of the universe. He could make planets collide and produce his suns and stars, his heat and light; he could originate life in all its infinite forms. To cause at will the birth and death of matter would be man's grandest deed, which would give him the mastery of physical creation, make him fulfill his ultimate destiny.

Book I, lines 82–83 (tr. C. Bailey)
De Rerum Natura (On the Nature of Things)

Sunday Times interview (1990)

Epistulae Morales ad Lucilium (Moral Letters to Lucilius), Letter XXIV: On despising death

Context: You have enemies? Why, it is the story of every man who has done a great deed or created a new idea. It is the cloud which thunders around everything that shines. Fame must have enemies, as light must have gnats. Do not bother yourself about it; disdain. Keep your mind serene as you keep your life clear.

Villemain (1845)

"Whether Genius is Conscious of its Powers?"
The Plain Speaker (1826)

Book 7, Ch. 50.
The Histories

Source: The Revival of Aristocracy (1906), p. 39.