Interview by Kevin Rose
The benefit of "first principles" thinking? It allows you to innovate in clear leaps, rather than building small improvements onto something that already exists. Musk gives an example of the first automobile. While everyone else was trying to improve horsedrawn carriages, someone looked at the fundamentals of transportation and the combustion engine in order to create a car.
Naturally Musk does give one warning about using first principles for innovating however, "it takes a lot more mental energy."