My favourite quote is from Winston Churchill during some fo the bleakest days for Britain in WWII. I find it especially relevant to startups and entrepreneurs, much like the audience of HN itself.
"I was sitting on the seashore, half listening to a friend arguing violently about something which merely bored me. Unconsciously to myself, I looked at a film, of sand I had picked up on my hand, when I suddenly saw the exquisite beauty of every little grain of it; instead of being dull, I saw that each particle was made up on a perfect geometrical pattern, with sharp angles, from each of which a brilliant shaft of light was reflected, while each tiny crystal shone like a rainbow.. The rays crossed and recrossed, making exquisite patterns of such beauty that they left me breathless.... Then, suddenly, my consciousness was lighted up from within and I saw in a vivid way how the whole universe was made up of particles of material which, no matter how dull and lifeless they might seem, were nevertheless filled with this intense and vital beauty. For a second or two the whole world appeared as a blaze of glory. When it died down, it left me with something I have never forgotten and which constantly reminds me of the beauty locked up in every minute speck of material around us." -- George Russell
"How strange is the lot of us mortals! Each of us is here for a brief sojourn; for what purpose he knows not, though he sometimes thinks he senses it. But without deeper reflection one knows from daily life that one exists for other people -- first of all for those upon whose smiles and well-being our own happiness is wholly dependent, and then for the many, unknown to us, to whose destinies we are bound by the ties of sympathy. A hundred times every day I remind myself that my inner and outer life are based on the labors of other men, living and dead, and that I must exert myself in order to give in the same measure as I have received and am still receiving..." - Albert Einstein
"Mathematics, rightly viewed, possesses not only truth, but supreme beauty—a beauty cold and austere, like that of sculpture, without appeal to any part of our weaker nature, without the gorgeous trappings of painting or music, yet sublimely pure, and capable of a stern perfection such as only the greatest art can show. The true spirit of delight, the exaltation, the sense of being more than man, which is the touchstone of the highest excellence, is to be found in mathematics as surely as in poetry. What is best in mathematics deserves not merely to be learnt as a task, but to be assimilated as a part of daily thought, and brought again and again before the mind with ever-renewed encouragement. Real life is, to most men, a long second-best, a perpetual compromise between the ideal and the possible; but the world of pure reason knows no compromise, no practical limitations, no barrier to the creative activity embodying in splendid edifices the passionate aspiration after the perfect from which all great work springs. Remote from human passions, remote even from the pitiful facts of nature, the generations have gradually created an ordered cosmos, where pure thought can dwell as in its natural home, and where one, at least, of our nobler impulses can escape from the dreary exile of the actual world." - Bertrand Russell
“A lesson without pain is meaningless. That's because no one can gain without sacrificing something. But by enduring that pain and overcoming it, he shall obtain a powerful, unmatched heart. A fullmetal heart.”
― Hiromu Arakawa, Fullmetal Alchemist, Vol. 25
"The society which scorns excellence in plumbing as a humble activity and tolerates shoddiness in philosophy as an exalted activity will have neither good plumbing nor good philosophy; neither its pipes nor its theories will hold water." J. Gardner
"If you're going through hell, keep going"
You can read more about the history behind it and the context here: http://www.forbes.com/sites/geoffloftus/2012/05/09/if-youre-...