From PayPal through to SpaceX and Tesla Motors, Elon Musk has become the epitome of Tony Stark (minus the shiny red suit). When Musk speaks, it is usually a good idea to listen, especially when he is talking about innovation - this is especially true on his appearance on Kevin Rose's Foundation series.
First Principles is a concept taken from physics that Musk applies to much of the innovations in his recent efforts. The concept is simple, start with the fundamentals you know are true, and work up from there.
"It's important to reason from First Principles rather than by analogy. So the normal way that we conduct our lives is that we reason by analogy. We are doing this because it's like something else that was done. Or it's like what other people are doing.
It's mentally easier to reason by analogy, rather than from first principles. First Principles is kind of a physics way of looking at the world, and what that really means is that you boil things down to the most fundamental truths, and say what we are sure is true, or sure is possible is true. And then reason up from there - that takes a lot more mental energy.