For over half a century, runners had been trying to break the 4-minute mile. Then, in 1954, Roger Bannister finally ran a mile in 3 minutes and 59.4 seconds. And then, just 46 days after Bannister showed that it could be done, another runner did it.
Since then, over a thousand runners have beat the 4-minute mile. It shows how much of what we think is physically and practically impossible is psychological. What holds us back is often our mindsets.