Marathon runners don't get enough credit for how insane their sport is. The pinnacle of easy to learn, hard to master.
At two hours, the pace is around 13 mph (21 kmh).
For perspective, go to your local gym/sports club, hop on a treadmill, and crank it to the highest speed setting. Chances are good that it'll top out at 10 mph and you'll be pressed to run that for more than a minute.
Now, add 30% more speed to that and you're close to what these folks crank out. For hours.
Absolutely mindboggling.
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.)