“When I got there, boarding had closed and I could see the last passengers in the bellows boarding the plane. I was demanding to get in too, but they didn’t allow it,” Mr. Mavropoulos said on Monday.

Three hours later, as he was boarding the next flight to Nairobi, two security guards escorted him to the airport’s police station, over his loud protests — he did not want to miss his meetings in Nairobi.

But an official explained that he should “stop protesting and thank God,” instead. They could not let him leave before they had established who he was and why he had not boarded the flight, which had crashed.

Mr. Mavropoulos was shocked.

“The thoughts came like streaks of lightning: ‘Oh my God,’ ” he said. “I’m alive because the connection ambassador was a few minutes late, and then that I was demanding they’d let me in the flight — imagine what would have happened if they had done so.”

Image A picture of the ticket that Mr. Mavropoulos posted on social media. Credit... Antonis Mavropoulos

He realized he should contact his family, let them know that he was not on Flight 302, that small, random events had made him miss it: not having a suitcase, missing the airline representative, running late. A spokesman for Ethiopian Airlines confirmed on Monday that Mr. Mavropoulos’ booking was changed to the 4:25 p.m. flight from Addis Ababa to Nairobi.

He thanked his good fortune for what he had berated as bad luck. “I broke down the moment I had that thought,” he wrote.