Okay, so I'm running a 5k at the end of September on campus (the Waterloo Homecoming AHS fun run) and I'm more intimidated by that run than my 15k at the end of October! Why you might ask? Because I'm a long distance runner.
I believe that runners come in two types. The first I call speedy sprinters like my hubby and running BFF who have long legs, take long strides and can zip off and do a short 5 or 10k really powerfully. When my husband runs a long race he usually goes out of the starting gate really strong and then slows down as he runs, and gets passed by a lot of runners at the end of the race. He improves his times in the long races, as he does them but he has a hard time pacing himself on long runs. But when he does a shorter run he can push himself and do a great job. Though he'd probably disagree with me, and say he can't go hard enough for short distances, but now that he's learned how to do speed training he'll rock his next shorter race.
The other kind I call power runners, who like me don't always have the strength to really push it out of the gate, but instead have the ability to pace themselves and can actually push harder at the end of a 21k than at the start. I do not have the ability go push myself hard enough to do any decent time in a 5k but I can rock a 21k. I manage to get through a long race and still have the umph at the end to pass people. In my Waterloo Half-marathon I passed four or five people in the last few kms and in St.Catherine's I passed nine (I actually counted because I was so proud to be passing people).
Honestly, I'm not just crazy about my distance theory, I have math to back this up. My pace at the Waterloo Classic (10k) was 7:14 and my pace at the Run for the Grape (21k) was 7:06. Both had a similar little hill and were city races. If anything the Run for the Grape, went into the country which provided more stuff to look at and distract me, and had a pit stop in it which is counted in the pace. So while my little legs can't push myself crazy hard for 5 or 10 km straight, they can do it for a few km and then do a little bit slower and then push again soon after. I need a small amount of recovery time to restart my crazy speed push, which a long race allows you to do!