"What is a magican but a practising theorist?" -- Obi-Wan Kenobi 
"Do, or do not. There is no 'try'." -- Yoda 
"Ah, but a man's reach should exceed his grasp. Or what's a heaven for?" -- Robert Browning 
"I find that the harder I work, the more luck I seem to have." -- Thomas Jefferson 
"What Des-Cartes did was a good step. You have added much in several ways, & especially in taking ye colours of thin plates into philosophical consideration. If I have seen further it is by standing on ye shoulders of Giants." - Isaac Newton (to Robert Hooke)
"On quantum theory I use up more brain grease than on relativity."  -- Einstein
"I like being a novelist for the same reason that Charles Dickens liked being a novelist.
You can play all the parts, arrange the scenery, be the whole show and nobody gets in the way." -- Robertson Davies [please substitute economic theorist for novelist] 
"I never underestimate the power of a theorist to come up with a new model."
--  Saul Perlmutter (physicist, Lawerence Berkeley National Labs) 
"Basic research is what I am doing when I don't know what I am doing." -- Werner van Braun 
"Research is the process of going up alleys to see if they are blind." -- Marston Bates 
"I have gone into projects out of a personal belief that we can so do something special that we can be proud of. Successful entrepreneurs never cost out a project. They have a vision that something is not being done properly and they can so it better." -- Richard Branson 
"Far better it is to dare mighty things, to win glorious triumphs even though checkered by failure, than to take rank with those poor spirits who neither enjoy much nor suffer much, because they live in the gray twilight that knows not victory nor defeat."
-- Theodore Roosevelt 
"You have to know how far you can get. Something that hasn't been done. And there is no one else who can do it -- because no one else can do you." -- Jerry Seinfeld
"There is no likelihood that man can ever tap the power of the atom."
-- Robert Millikan (Nobel Prize winner in physics, 1923) 
"Heavier-than-air flying machines are impossible." -- Lord Kelvin, 1895 
"It's kind of fun to do the impossible." -- Walt Disney 
"To understand recursion one must first understand recursion."  -- stolen 
"Nothing shocks me. I'm a scientist." - Harrison Ford as Indiana Jones 
"Aristotle maintained that women have fewer teeth than men; although he was twice married, it never occured to him to verify this statement by examining his wives' mouths."
-- Bertrand Russell, on the scientific method