The marathon is so long with room for unique times and moments. A 5k is just as difficult as the marathon, with little room for being off pace. I would rather race a marathon and try to run a fast time than a 5k, because it's harder to place high in a 5k than a 26 mile race.
Does the quarter mile matter? If you run 1:15 you could have a 2:30 half mile. Then does the half mile matter? If you run 2:36 and 2:36 you could run a mile in 5:12.
How did I figure out how to pace myself in the marathon?
Well, the first time I went on a 20 mile run... I did my ten mile course two times in a row. I looked at this as 5 miles at a time. However, in my first 26.2 mile race after running 13.1 miles I felt uncomfortable trying to run it all over again. The reason a 26.2 mile course difficult, is not just because of it being 6 miles more than my uncomfortable zone. I always train in five mile increments, where I am familiar with running. So, my tip is running a mile out of your normal routine somewhere new while trying to stay on pace.
One mile more somewhere new is always a challenge. Think about new places and trying to run a little bit further to be ready for a full marathon.
It is still tempting to go out too fast the first fifty meters of a race and tear my quads. I know next month I'll be toeing the line for my 26.2, and have to stop myself from going out in a dead sprint trying to be in front of everyone there.
It's silly to sprint in the beginning of a marathon, when there are over twenty miles to pace yourself for. You really need to commit to your finish time on the starting line, and maintain an even pace throughout the entire event. With that being said, every runner should have layers of goals.
So, if I fall off pace and negative splits will not catch me up to my goal the solution is, ten minutes of wiggle room as well as a goal of placing in my age bracket.
The further your event, the more you will think about how many 6 minute miles could you run in a row? How many 7 minute miles could I run in a row? Am I too young to run 8 minute miles? Is walking okay, ever?
Pacing yourself is a lifelong learning experience.