The four minute mile.
Athletes had been trying to achieve it since the ancient Greeks.
All the experts said it was impossible: our bone structure was wrong; wind resistance too great; lung capacity inadequate.
Then one man came along and proved all the doctors, the coaches, the naysayers and the countless men who'd tried and failed before him all wrong.
On May the 6th 1954 on the running track at Oxford University, Roger Bannister ran the mile in 3 minutes 59.4 seconds.
Just forty-six days later a second athlete broke the four-minute mile. And the following year, many more.
What happened? The human body didn't suddenly improve, but the human spirit did.
As Bannister recalled half a century later:
"No longer conscious of my movement, I discovered a new unity with nature. I had found a new source of power and beauty, a source I never dreamed existed."
He was in what today we rather less eloquently call 'the zone.'