How well do you know your main character? Do you know his/her deepest longing? If your answer is no, you need to stop and take a closer look at your character arc. What is motivating your character? If you can identify that, you know their core desire.
Does he/she want to be loved or save the world? Does he/she want to be respected or rich? Whatever the desire, it has to be something your reader can relate to.
Your character may have more than one desire. I know most of us do, but our minor desires usually lead us to our core desire. That one thing that we really want more than anything.
A great example I read described a young girl who was abused by her father. As you probably guessed, her core desire was to be loved by him, or maybe you thought to get even. Not sure how your mind works 🙂 At any rate, the only thing he seemed to be interested in was astronauts and space exploration. So the young girl set her sights on becoming an astronaut. Now she may have found her studies fascinating and developed an interest in space along the way, but her goal was to earn her father’s respect and love by becoming the one thing that piqued his interest.
After you’ve identified your main character’s core desire and put him/her on the path of achieving it, the fun begins. What can be thrown in to threaten his/her core desire? What can throw him/her off, and how can it be fixed?
You have to know your character’s core desire. It helps you understand what kind of things he/she will seek in life, and what kind of things can mess his/her life up.
Something to think about.