Jim McKelvey co-founded mobile payments tech giant Square, founded social venture LaunchCode, is a venture capital investor at Cultivation Capital and is a glassblowing artist with works featured in the Smithsonian and the Museum of Modern Art. He is, across almost any number of metrics, a formidable success.

However, McKelvey is not without fear. He got weak knees and sweaty palms when he was asked to take the stage after the iconic General Electric manager, Jack Welch, at a conference in Copenhagen.

“Jack Welch is a legend. He is one of my personal heros, and a super brilliant and nice guy,” McKelvey said during the 3686 South conference in Nashville last week. Despite his own remarkable success both in Silicon Valley and in the glassblowing studio, McKelvey felt totally unequipped to follow Welch on stage. “Jack Welch turned around the biggest company on the planet, named manager of the century, nicknamed after a nuclear device: Neutron Jack. How cool do you have to be to be nicknamed after an atomic weapon?”

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McKelvey begged the conference organizers to change the schedule for the program so that he could go before Neutron Jack. The conference organizers refused, professing that the conference programs were already printed. Welch, who is 80, started speaking.

“And this guy sits down on his chair and this guy crushes it! He is awesome! He loses 20 years on stage," McKelvey said. "He is funny, witty, his stories are awesome. He is just killing it.”

McKelvey’s anxiety mounted. Unable to sit still with his fears, McKelvey turned to the gentlemen sitting next to him as he was waiting to go on stage and confessed his mounting anxiety. The Danish fellow says, “Oh, Jack! Here in Copenhagen, we love Jack Welch. We have all read his books. We have all implemented his theories. None of it works!”

McKelvey swung around and did a double take. That moment provided a powerful lesson for McKelvey, and it has affected how he thinks about his own career.

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“Here’s the problem from taking any advice from anyone who has been successful: You don’t know how much of it is luck," he said. "I honestly can’t tell you how much of the stuff I have done has been because I am really hardworking and smart, which I like to think, or because I was just lucky in that case.”

When people are successful, they may end up reverse engineering reasons for their achievements. In reality, however, it may be complicated to replicate that path. If McKelvey has been lucky, he has been exceptionally lucky. Square is worth almost $3 billion.

“Nothing against Jack Welch, but what he did worked for GE at a period of time that was unique. And he has fantastic advice, I love his books, I like the man, he is brilliant," McKelvey said. "And yet, even advice from the manager of the century may not be relevant for somebody is struggling with a problem today. To anyone who is listening, yeah, OK, listen. But listen skeptically.”