Here's an example. Put a rat in a maze. Have a piece of chocolate at the exit of the maze. The rat will smell it and find a path to the chocolate. After repeating this a few times, the rat will learn the correct path and go there over and over again, faster each time. The rat will take some wrong turns and maybe get lost, but will eventually gain the skill of manoeuvring through the maze.
You are more intelligent than a rat. Your brain is very plastic (changeable/moldable). You can learn much faster.
However, without the piece of chocolate, the rat would probably never learn the path out of the maze, except by chance. Most of us, in trying to gain a skill often forget to put the rewards in the end of the maze. We find the path there out of chance. Studies show that most people who become avid exercisers do so out of boredom. The others often have a goal in mind, like looking good enough to get a mate. A lot of people forget about exercise because they see no results in a short period of time.
The key is to reward yourself. Unlike a rat, you are smart enough to know that at the end of the maze lies endless opportunities for more rewards. But you still need to have a reward at the end to go there at all.
It doesn't have to be a big reward. Even a positive feeling works just as well as a reward as getting a car. One of the bonuses of doing something with a friend is that you can discuss the difficulty of the task with them and mutually praise each other or learn how to do it faster. The fact that you've completed the routine at all is a reward. But you have to get positive feedback of some sort.
If possible, try to break down your learning into smaller tasks or checkpoints. If you're learning to run, record how much time you take to go a certain distance. If you're reading a difficult book, your rewards might be in completing a chapter or the exercises at the back of the chapters. Make sure that you have a clear feeling that you're making progress of some sort.
Don't worry too much about the injuries and setbacks. They happen. You had to fall a few times to learn to walk. Sometimes you even banged your jaw on the table. You had people laughing at you if you learned a second language or tried to play a musical instrument. Accept it as part of the process.