"Sometime toward the end of my second year, I started working with Gell-Mann. I went to Gell-Mann and he gave me a problem to work on and suggested I start working with fixed source theory of K-particles, where he wanted me to do things involving strong and weak interactions. And it's when I read about fixed source theory that I began to learn about renormalization group and realized it could be applied to fixed source theory, and I don't know whether there were papers that I read about renormalization group and fixed source theory, or I worked it out for myself, but in playing around with this, sort of trying to learn what was going on, I discovered that there were great simplifications that took place when you took the fixed source equation and took them to high energies, and when you did a leading log approximation. In the end, I discovered that those equations, simplified at the high energies -- you could get exact solutions. That was part of my thesis. And that was the initial thing that sparked my interest in the renormalization group. I remember when I presented my thesis to a seminar, and this was when Feynman was there, but not Gell-Mann. I went through all this exciting mathematics and toward the end, someone said, "Yes, that's fine, but what good is it?" I remember Feynman's answer as "Don't look a gift horse in the mouth!""