There are two aspects to conquering a distance. The first phase is the ability to complete the distance. Most runners who train for a half marathon or a full marathon only train enough to do this phase. They complete their race, but they typically suffer soreness, pain, and perhaps injuries during and after the race. Some of them get discouraged and give up on distance running.
The second phase is your body being able to handle the stress of the distance, such that the distance is now a "breeze in the park" so to speak. It takes doing the distance several times before your body becomes strong enough to handle the stress. Most marathoners only accomplish this phase after running several half or full marathons. Many people only complete one or two marathons and never accomplish the second phase. We're all different, and some people accomplish this phase after running the distance two or three times, while other people need many repetitions of the distance before their body can handle the stress.
Today was my 3rd time to run 10 miles, and I think I'm starting to get used to that distance. I'm not claiming that my body has gotten used to the 10-mile distance, but I think it is starting to do that. I felt better today after completing the run than I did after my first two times of doing that distance, although I'm still tired after doing 10 miles. I forgot to take a short nap when I got home from my run, and I sorta moped around and didn't do much for the rest of the day.