I have just browsed much of Adventures in the Atomic Age: From Watts to Washington by Glenn Seaborg, a Nobelist in Chemistry. He quoted in passing Tom Landry's

I have just browsed much of Adventures in the Atomic Age: From Watts to Washington by Glenn Seaborg, a Nobelist in Chemistry. He quoted in passing Tom Landry's dictum that "You can't think and smile at the same time.", but in the context of saying that some can: Enrico Fermi was always smiling, and always thinking.