In a Georgian townhouse in central London, Alexis Stenfors stood before a roomful of University of Iowa students.

After 15 years as a successful trader at several big banks, the 44-year-old Scandinavian was accustomed to high-pressure situations. At home, he had rehearsed his presentation again and again, trying to gain comfort with an uncomfortable topic. He had practiced in private, not even letting his wife hear what he planned to say.

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