https://www.wired.com/story/how-the-boston-marathon-messes-with-runners-to-slow-them-down/

The Boston Marathon course looks like it should be fast. You start out in the distant suburb of Hopkinton—elevation 490 feet above sea level—and then cruise steadily downhill until about mile 9. The finish line has an elevation of a mere 10 feet above Boston Harbor. Fans pack the sides cheering you on. The route is pretty straight, west to east, with few 90-degree turns of the sort that slow your momentum. The road is asphalt, which is more forgiving than concrete.

So when the gun goes off Monday morning for the 123rd running of the race, everyone should feel good about hitting a personal best, right? Of course not. As every veteran marathon runner knows, Boston is slow, wicked, and tempestuous. It’s a wonderful course if you want to experience camaraderie, history, and emotional uplift. It’s a terrible course if you want a personal best.