My best time was 11.9 seconds. The 100-meter-dash winner in the 1896 Olympics was Thomas Burke, who won with a time of 12 seconds flat.
I did cross-country for three years in high school and ran track (pole vault, mostly) for nearly six, going partway into college. But in all that time, I never got past the point where going out and running 3 miles felt hard. It was always unpleasant at best.