Do we ever really know what motivates us day-to-day in creative projects? What's 'free will' do we think we're using?

(The book referenced is Sincerity: How a Moral Ideal Born Five Hundred Years Ago Inspired Religious Wars, Modern Art, Hipster Chic, and the Curious Notion that We All Have Something to Say (no Matter how Dull) https://www.google.com/books/edition/Sincerity_How_a_moral_ideal_born_five_hu/dZh3DB7jj5wC?hl=en&gbpv=0