One of the greatest challenges I have is getting folks to switch from reactive to proactive behavior with their horse.
Although for a majority of people riding is supposed to be a fun outlet or escape from other aspects of their life, it isn't always the romanticized experience that initially inspires most folks to start riding in the first place. But it can quickly become an emotionally frustrating experience when the human has intentions that may not yet be appropriate for their own abilities or that of their horse.
I can't count how many people I meet that seemed to have woken up one day and randomly decided to start doing something with their horse and then wondered why it ended in disaster.