A long-run is a huge challenge for your brain. Running beyond a certain point will feel tiring to your mind. So you have to train it, figure the tricks, and learn some techniques to enjoy your long runs. Here are some things to remember:
As you keep running, you'll learn the tricks your mind tries to play on you.
"The only one who can tell you 'you can't' is you. And you don't always have to listen!"