If a good cook is asked to share her recipe for a great meal, and she knows you know nothing about her, her history, her lifestyle, her shopping habits, she'll tell you what products she used and how she combined them. She may even give you the step-by-step instructions.
If you asked her why she prepared this meal on this occasion, she'll be speechless. Too much to analyze and distill for your ears. Her whole being and history worked the magic to bring this meal to you. That part called motivation is hidden inside her dreams and aspirations, and the dreams and aspirations of her ancestors. I'm most serious about this. Ask me why I prepare my pasta and beans on Mondays and I can give you the history of four generations.
Ask a poet, a novelist how to recreate that poem, that novel, and he/she will not be able to guide you much. He'll tell you it is a progression of insights you have to discover yourself. It is a butt-on-seat tenacity, it is all the books you read and absorbed. It is the love you have hidden in you; all your ideas lined up to exit through a few thousand words.
Most of all, he'll say, it is a passionate act, a sharing of great magnitude, an act of confession. A work of art will speak like no other work. It will tell a story. Evoke hidden feelings. Create a universe where you the reader are also sharing and confessing your innermost thoughts.