When writing a story, don't write a plot. Instead, write a setting where such a plot can occur. This will increase your story potential and force you to think more deeply about your characters. Other authors and myself have seen this multiplying affect. It can work for you as well.
When I first began writing Eric's story, I realized that I didn't have the setting to support the story. So I created a setting that would enable Eric's primary plot, A Mage's Power. Then I split the second book in two because I saw more story potential within this setting. Thus, Looming Shadow separated from Mana Mutation Menace. While writing Clerics at Work (the tentative title of book 4), I had to go back and re-write two arcs because they had developed into more than arcs. The story potential of the setting Eric was in, or the story behind a side character, was becoming its own story. I will have to re-write the vast majority of book 5 (tentatively titled "The Highest Power") because I was so interested in this new area of the setting and the story potential of its people, that Eric's narrative became lost.
The ways the characters of Tariatla interacted with each other grew more and more numerous. The history of a given location or event developed potential great enough for their own books. I couldn't use all of them in the series. "Journey to Chaos" is supposed to be Eric's journey after all. Then I thought, why not? I have the setting and the characters, so I'll just split all the plotlines up into their own books.
I created the world of Tariatla exclusively for Eric Watley, my first protagonist, and his adventures. Any other characters I had or plots I planned happened in other worlds. Then I realized how well they could go together. Then there were two series set in Tariatla. I continued developing plots and realized that they too could fit within this setting. At that point I realized that by grouping plots together in the same world, I made them stronger. "The whole is greater than the sum of its parts", as the saying goes. By looking at aspects of the setting and how they can be used to create conflict, I could create new plots. By looking at side characters and pondering what their lives were like outside of what occurred in someone else's narrative, I could write still more. As of this writing, there are nineteen (19) Tariatla stories in various stages of development.
When you write a story, it's not about writing a plot. Plots are tricky beasts. Instead, write a setting where a plot can occur. It's like a board game; you create the board and the pieces and the rules. Then you write a story from the ways in which these factors interact.
A plot is a strict set of events that goes from beginning to end and then it stops. It bends setting and characters and rules into knots in order to make events happen the way that the author wants. This is the Hand of the Author. It interrupts immersion, breaks willing suspension of disbelief and gives rise to things like Idiot Balls. It's not organic but artificial. The setting and characters only exist for certain events rather than inherently creating events. It's a waste of potential. It's like throwing away a resusable container along with the trash.
Fate Stay Night is a good example of this; a stellar example. Fate Stay Night is a visual novel with three routes. These are three storylines that can take place depending on the actions of the player (as Shirou Emiya). All the routes have the same backstory, the same premise and the same characters. The only thing that changes are the ways in which they interact. Depending on the way the characters move about in the setting, the events and the result will change. It's amazing how the first route (Fate Stay Night) differs from the second route (Unlimited Blade Works). I've heard that the third route (Heaven's Feel) is also different.
Furthermore, the main series has spin offs such as Fate Zero and Kaleid Liner Prisma Illya which use the same setting and characters but tweak a couple things to create a new plot. Fate Zero, for instance, takes place during the previous Holy Grail War that was fought by the previous generation. Kaleid Liner Prisma Illya focuses on a side character in the main Fate game, Illyasviel von Einzbern, and her own version of the Holy Grail War.
A Certain Magical Index is another example. The initial stories are about Touma Kamoji and his adventures in Academy City. Then you get Accelerator's story which is focused on him and Last Order and doesn't include Touma at all. He gets a spinoff called A Certain Scientific Accelerator and so does Misaka Mikoto, in A Certain Scientific Railgun. All three of them are the same setting and the same characters, but each is focused on a different person, a different cast and a different slice of Academy City.
Touma sees the setting from the perspective of someone between magic and science, and as well as someone lacking the bulk of his memory. His take on events and people contrasts to Accelerator, who is compared to him like a foil. Accelerator stands at the height of science and what a lonely place it is. When the reader follows his path through Academy City it looks different. This is also true for Misaka, who is also high on the science side, and has her own views and challenges. These groups and their plots overlap. Each of them could be considered The Hero of Another Story to the others.
What's the Hero of Another Story? It is a character that experiences adventures in the same plot as The Hero. They share the same setting but one's adventures occur off-screen (or in a spinoff) as compared to the other. This trope plays a significant role in the second draft of Journey to Chaos book 4: Clerics at War. It's been fun to hint at the adventures of this off-screen hero. I might have to write a book explaining them some time.
Writing settings instead of plots leads to a better narrative. The story potential is multiplied and the interaction of the character development and interaction is more organic and complex. I have experienced this and so I recommend it.