I Believe People Come Into Your Life For a Reason

Like a fast paced action adventure story, where characters are introduced, developed, and removed all in hopes to progress the story, there are very similar truths to real life. Every person that touches your life adds details and dynamic to your story. Some you may love and cherish, others you may hate, some bring joy while others pain, but each ultimately altered your path in some shape or form. So is it really crazy to believe that some people are only in your life to teach a lesson or progress the story? Coincidence is not causation but I would be lying to say the thought has not crossed my mind once or twice before.