Robert Cotter III was across the street eating breakfast when terrorists drove a commercial jetliner into the World Trade Center's North Tower.
But he didn't feel the thunderous collision. He didn't hear the screaming.
A waiter whispered the news in his ear while he ate. He didn't want to rattle the client Cotter was hosting.
At first, he assumed it was an accident. Probably a Cessna or something.
He hadn't heard the announcement over the loudspeaker. They were a common occurrence ever since terrorists had bombed the parking garage of the World Trade Center in 1993.
Then minutes after 9 a.m., he remembers hearing United Airlines Flight 175 pummel into the South Tower. It sounded like a nuclear bomb, he said.
He walked out of the building to find people covered in glass, dust, metal and blood. Unable to get to his 42nd-floor office, he headed north toward midtown Manhattan. He could feel the heat coming from dozens of stories up the burning towers.
Cotter, a 1969 graduate of McCallie School and current trustee of the school, ran up Broadway. He saw miscellaneous body parts lying in the dust-covered streets. After walking six or seven miles and after several hours, he was able to contact his wife to tell her he was alive.
"In a flash, the world became so much different from what it was before," he said, sharing his memories of Sept. 11, 2001 this week with McCallie students.
Cotter, who now lives in New Canaan, Conn., told McCallie students that the day taught him the importance of tolerance - and the destruction of intolerance.
"Even if they're different," he said, "remember that there is plenty of room in the world for all of us."