Source of book image: http://images.amazon.com/images/P/0738203491.01.LZZZZZZZ.jpg
In his elegant and thoughtful foreward, physicist, futurist, and guru Freeman Dyson writes:
(p. viii) Before I met Feynman, I had published a number of mathematical papers, full of clever tricks but totally lacking in im-(p. ix)portance. When I met Feynman, I knew at once that I had entered another world. He was not interested in publishing pretty papers. He was struggling, more intensely than I had ever seen anyone struggle, to understand the workings of nature by rebuilding physics from the bottom up.
The reference to the book, is:
Feynman, Richard P. The Pleasure of Finding Things Out: The Best Short Works of Richard P. Feynman. New York: Perseus Books, 1999.