I wouldn’t go that far. You fall on the Trollope side of the equation, where the novel is a journey for the writer as well as the reader. The Wilkie Collins side (where it is pre-planned down to the last detail in advance) is equally valid.
It was the practice of Wodehouse, that sublime master, to write about 400 pages of notes before attempting so much as an opening paragraph. A good plot is a complex thing, and even a practiced professional with formidable natural gifts must struggle to devise a perfect one.