Cross-country is all about recovery. On most courses, you will encounter sections of the course (usually hills) that are harder than others. The runners that finish highest are the ones who can recover best after each of those hard parts and continue pushing through the race.
This is hard to do.
Fortunately, you will not be running in one of those drawings by Escher where you could just keep going uphill. Eventually, you have to come back down. During a race, you have to trust that your fitness will enable you to recover enough to continue racing as hard as you can. That trust is difficult to summon, but once you experience it, you can definitely use it to your advantage. When many runners, especially those newer to the sport, reach the top of a hill, they often sort of breathe a sigh of relief and pause slightly. That's when you can burst ahead of them, knowing that, while, yes, you are dying, too, you will survive and even feel better in a minute or so.
Try it next time....