"Finish each day and be done with it. You have done what you could. Some blunders and absurdities no doubt crept in; forget them as soon as you can. Tomorrow is a new day; begin it well and serenely and with too high a spirit to be encumbered with your old nonsense."

—

One of my favorite quotes, from Ralph Waldo Emerson. Everyone working in a startup should read this every morning.

http://www.goodreads.com/quotes/18830-finish-each-day-and-be-done-with-it-you-have