Book ideas come from many experiences and lessons of those traumatic and joyous times. Considering my writing of fiction I will venture in retrospect, from experiences both in body and out of body. Actual personal experiences and observation of other peoples experiences, both personally viewed and orally sensed. Reading is a great avenue toward inspiration in a manner of what might be done to concoct a story leading to the beginning of what you read or after what you read, in the same vein or a different view or a new writing experience.
I believe most readers are left wanting when the story being read ends, because it hasn’t really ended. It began in some far away time and the author relayed the trials and tribulations and the points of interest of a characters life, actions, desires, dislikes, frustrations, joy, failures, achievements, relationship(s) with the painting in a picture of words in a specific time frame. What brought the character to that specific time frame? Who helped mold the character and how was the character brought to the point of life the specific time frame speaks of? What will an additional specific time frame have in store for the character and the possible cast of other characters in that recounting? That may be an avenue for the explanation of where book ideas come from.
What story would you read if you could find it? The answer could be where book ideas come from. If the answer is that you never have found the story you want most to read, write it in a specific time frame, but do not limit the telling of the story if it requires pages that bring an epic number of pages to the telling. The world is yours to paint as you wish in different intervals of time. As frail individuals our failure to do as we may desire is lost for that specific time frame and the beautiful accumulation of words is nothing except a never written vague memory. Even words formed and written today can never be penned in the same way in another specific time frame. I could never again write the novels I have published to bring about the exact manuscript. If I had not written them they would have no birth and no existence for future generations to enjoy. (I hope).
Start with a single sentence. That may or may not eventually be your beginning, but the journey has a start when those words are recorded. Dump the depressing thought that your work will not be as well received as one of the prominent authors. Their first draft was as poor as any other, as evidenced by one of the greatest authors. It was enhanced and rebuilt and God only knows how much time and effort went into making it as it finally became. You should write for the absolute joy of doing it, to be first. Motive be gone. Joy, joy joy, deep in your heart and cognitive recognition. You will construct a piece of literary genius, no matter about magnitude or value. Yours alone. Enjoy reading the final manuscript and put on the armor needed to make it the best your ability and subsequent readers will do to bring your work to fruition. It will never be all you want. Let it be enough for others to enjoy and get busy with the next installment, such as my post civil war tale titled South of the River : https://www.smashwords.com/books/view/1176583 and Best Of Luck : https://www.smashwords.com/books/view/1144008 followed by Never Too Late : https://www.smashwords.com/books/view/1033739 Plus twenty-seven soon to be enjoyed works of fiction by my hands.