“No man can fully grasp how far and how fast we have come, but condense, if you will, the 50 thousand years of man's recorded history in a time span of but a half-century. Stated in these terms, we know very little about the first 40 years, except at the end of them advanced man had learned to use the skins of animals to cover them. Then about 10 years ago, under this standard, man emerged from his caves to construct other kinds of shelter. Only five years ago man learned to write and use a cart with wheels. Christianity began less than two years ago. The printing press came this year, and then less than two months ago, during this whole 50-year span of human history, the steam engine provided a new source of power. Newton explored the meaning of gravity. Last month electric lights and telephones and automobiles and airplanes became available. Only last week did we develop penicillin and television and nuclear power, and now if America's new spacecraft succeeds in reaching Venus, we will have literally reached the stars before midnight tonight.
This is a breathtaking pace, and such a pace cannot help but create new ills as it dispels old, new ignorance, new problems, new dangers. Surely the opening vistas of space promise high costs and hardships, as well as high reward.
So it is not surprising that some would have us stay where we are a little longer to rest, to wait. But this city of Houston, this state of Texas, this country of the United States was not built by those who waited and rested and wished to look behind them. This country was conquered by those who moved forward — and so will space.”

Evolution (1895; 1909)
Context: And that was a million years ago
In a time that no man knows;
Yet here tonight in the mellow light
We sit at Delmonico's.
Your eyes are deep as the Devon springs,
Your hair is dark as jet,
Your years are few, your life is new,
Your soul untried, and yet

"The Individual and Political Life of Information Systems", in Heilprin, Markuson, and Goodman, ed., Proceedings of the Symposium on Education for Information Science, Warrenton, Virginia, September 7-10, 1965 (Washington, DC: Spartan Books, 1965)

Source: Guns, Germs, and Steel: The Fates of Human Societies

Source: The Fountainhead

Source: The Jewels of Aptor (1962), Chapter X (p. 133)
Context: A lesson which history should have taught us thousands of years ago was finally driven home. No man can wield absolute power over other men and still retain his own mind. For no matter how good his intentions are when he takes up the power, his alternate reason is that freedom, the freedom of other people and ultimately his own, terrifies him. Only a man afraid of freedom would want this power, who could conceive of wielding it. And that fear of freedom will turn him into a slave of this power.

… We looked at each other, me and my friends, and we were, like, when we’re 86, we want to be like that …. So that’s what started it.
" Jeru the Damaja http://www.peta2.com/heroes/jeru-the-damaja/", interview by Peta2, having just released his album Divine Design (2003).

citation needed

Attributed to Plato in Confidence : How to Succeed at Being Yourself (1987) by Alan Loy McGinnis, this is probably a paraphrase of a statement which occurs in Letter of Advice to a Young Gentleman Leaving the University Concerning His Behaviour and Conversation in the World (1907) by Richard Lindgard: "Take heed of playing often or deep at Dice and Games of Chance, for that is more chargeable than the seven deadly sins; yet you may allow yourself a certain easie Sum to spend at Play, to gratifie Friends, and pass over the Winter Nights, and that will make you indifferent for the Event. If you would read a man’s Disposition, see him Game; you will then learn more of him in one hour, than in seven Years Conversation, and little Wagers will try him as soon as great Stakes, for then he is off his Guard."
Variants:
You can learn more about a person in an hour of play than in a year of conversation.
Attributed to Plato in Food Is the Frosting-Company Is the Cake (2007) by Maggie Marshall
You learn more about a person in an hour of play than in a year of conversation.
Attributed to Plato by former Alaska Gov. Sarah Palin, as quoted in "Aspiring philosopher Palin quotes 'Plato'" (9 July 2009) http://thinkprogress.org/2009/07/09/palin-plato/
Misattributed

Il faut vingt ans pour mener l’homme de l’état de plante où il est dans le ventre de sa mère, et de l’état de pur animal, qui est le partage de sa première enfance, jusqu’à celui où la maturité de la raison commence à poindre. Il a fallu trente siècles pour connaître un peu sa structure. Il faudrait l’éternité pour connaître quelque chose de son âme. Il ne faut qu’un instant pour le tuer.
"Man: General Reflection on Man" (1771)
Citas, Questions sur l'Encyclopédie (1770–1774)