[jfengel]

Another way to put it: a 4 minute mile is 15 mph. The four minute mile was itself a "barrier" at one point. This guy did an average of 4:35 minutes/mile... 26 times in a row.

4:35 is a good time for your high school track team. Not a great time, but it'll probably get you onto the varsity team. But you only have to do it once.

And that's without even considering "the wall", which makes everything after mile 20 so, so much harder. I myself slow down by as much as a factor of 3 at mile 20. (Not that I'm a great marathoner.)