Well, we’d just been crawling around the floor — with help from some other people — trying to use meter rules to measure some feature of a giant printout of it. And Feynman took me aside, rather conspiratorially, and said, “Look, I just want to ask you one thing: how did you know rule 30 would do all this crazy stuff?” “You know me,” I said. “I didn’t. I just had a computer try all the possible rules. And I found it.” “Ah,” he said, “now I feel much better. I was worried you had some way to figure it out.”

Source: My Time with Richard Feynman — Backchannel