The top 100 ranking is just my personal opinion. Joseph Campbell's Hero With A Thousand Faces was rated among the most important of the 20th century by a group of experts, and for good reason.
It's hard to find a screenwriter or movie making company that does not follow Campbell's model for the hero's journey. Campbell took what had been also described as the monomyth-- the universal story, told with the same basic pattern, by every culture, about the journey of the hero.
This monomyth is a profoundly powerful description of the process of growth, of achieving a higher level of consciousness, of being reborn as a new, stronger person. It can also be applied to organizations and even movements.
It is a natural for moviemaking and has had several books written specifically focusing on using the concept to craft powerful stories with characters with depth. It is also used to help people and therapists conceptualize the process of going into therapy and healing, finding a new job, new relationships, new activism.
Ultimately, the hero's journey is a call to wake up and become a new person-- by making a choice, then developing new skills and resources, using them to face inner and outer challenges, then bringing back the "magic elixir" the final change, to the ordinary world you came from, to heal that world.
You can also consider the hero's journey to be a roadmap that explains the stages in the process of-- the journey of-- personal change-- a map that gives insight and understanding that can be invaluable.
The hero's journey goes through stages, which I'm abbreviating. Some of the stages include, with my own interpretation:
-call to adventure
-rejection of the call
-facing threshold guardians
-meeting the mentor
-crossing the threshold
-going underground or in the water-- symbolically
-starting on the road in the new world
-acquiring new skills and allies
-facing and battling antagonists
-meeting with the goddess
-at-one-ment with the father
-journey to the inmost cave-- almost dying, fighting the greatest antagonist
-Final successful confrontation
-straddling both worlds successfully
At the end, the hero can successfully live in both worlds.
Whole books have been written on just one stage in hero's journey. One of the best is Callings: Finding and Following an Authentic Life by Greg LeVoy.
And George Lucas used the Hero's Journey in his Star Wars movies, even getting to know Campbell.
This is a concept that you can apply to your life, whenever you face or desire to make change. Or use it for your writing for your stories or even for organizational change.
I've given lectures on it for groups interested in writing, for doctors who use it to conceptualize the treatment of patients, I've used it with individual clients, and for groups who are interested in personal growth.
The book is not a quick, easy read. It's one of a very few that I've read more than once. Consider it like a favorite nature site you love to visit. Return to it and you will discover new visions and ideas you missed before and previously seen ideas that you will see with new eyes, new perspectives.
Reading the book can be, just by itself, a hero's journey, since it will wake you up. Of course, you can refuse the call. When you refuse the call, by the way, very often, the call comes back to get you, more persuasively. Remember Obie Wan Kenobe? He asks Luke Skywalker nicely to join him to rescue princess Leah. Luke rejects the call. The next day, the aunt and uncle he lives with have been murdered by Darth Vader. Like I said, the "call" comes back to get you more persuasively.
If you want to get an easier read of the concepts in this book, try the The Writers Journey: Mythic Structure for Writers, 3rd Edition by Chris Vogler. Another excellent book that builds upon Campbell's concepts and Karl Jung's ideas is James Bonnet's Stealing Fire from the Gods: The Complete Guide to Story for Writers and Filmmakers\. One of the Top 100 Most Important Books of the 20th Century, Joseph Campbell's book is a treasure trove with a map inside that can help you understand some of the most important stages and journeys in your life. Or, you can use its ideas to write better stories.