“Start from scratch, stay patient, make a difference, and keep on improving.”
Related quotes

Industrial Revolution
Albums, Revolutionary Vol. 2 (2003)

"Reflections and Anecdotes", nr. 264 (Douglas Parmée translation)
Source: General systemantics, an essay on how systems work, and especially how they fail..., 1975, p. 65, cited in: Grady Booch (1991) Object oriented design with applications. p. 11

“If you wish to make an apple pie from scratch, you must first invent the universe.”
Source: Cosmos (1980), p. 218

“It makes a big difference in your life when you stay positive.”
Source: Seriously... I'm Kidding

1991 Chairman's Letter http://www.berkshirehathaway.com/letters/1991.html
Letters to Shareholders (1957 - 2012)

My Inventions (1919)
Source: My Inventions: The Autobiography of Nikola Tesla
Context: The moment one constructs a device to carry into practice a crude idea, he finds himself unavoidably engrossed with the details of the apparatus. As he goes on improving and reconstructing, his force of concentration diminishes and he loses sight of the great underlying principle.… I do not rush into actual work. When I get an idea, I start at once building it up in my imagination. I change the construction, make improvements and operate the device in my mind. It is absolutely immaterial to me whether I run my turbine in thought or test it in my shop. I even note if it is out of balance.
Source: Mathematicians are useful (1971), p. 1