"Keep your eyes on the stars, and your feet on the ground."

"Nine-tenths of wisdom consists in being wise in time."

"No man is justified in doing evil on the ground of expediency."

"If there is not the war, you don't get the great general; if there is not a great occasion, you don't get a great statesman; if Lincoln had lived in a time of peace, no one would have known his name."

"The only man who never makes a mistake is the man who never does anything."

"While my interest in natural history has added very little to my sum of achievement, it has added immeasurably to my sum of enjoyment in life."

"A plan is just a tangent vector on the manifold of reality."

"Forgive thyself little, and others much."

"A man's looks are measured by the depth of his pockets."

"The sum of all human wisdom is contained in these two words: Wait and Hope."

"I spend almost as much time figuring out what's wrong with my computer as I do actually using it."

"Never let the sense of past failure defeat your next step."