At the risk of sounding melodramatic (for how much drama could there be in an illustrator's life?), making a picture book is a bit like climbing a mountain. Many parts of the book illustrator's process parallels a physical attempt to summit a peak. Both can be measured in disciplined steps. There are months, even years of training, planning and preparation (that's the research, the writing, and the technique honing). There is acclimation and adjustments to be made (fitting rigorous deadlines into a family and social life accustomed to more flexible schedule). There is reaching certain camps and weigh stations along the way, for a mountain can't be climbed in a day. Base Camp I (storyboarding fits in here, the visual planning of a book), Base Camp II (detailed sketches to size next) Base Camp III (cover art perhaps) are all stages for each endeavor. There may also be necessary repeat trips back and forth from the camps, due to a number of unforeseen situations (edits, the flu, a broken boot cleat!). The journey to the top of Mt. Everest includes the notorious Death Zone, where the summit can be seen so tantalizingly close but slippery slopes still a hazard. It is hard work to stay focused. I'd apply this with final art making, hoping each stroke made is true to an initial vision.
And then to finish the set of pieces that, bound together, make a book. It must be akin to standing at the summit, taking in the sweet view and enjoying deep satisfaction of completing a long journey.
It won't be perfect, the climb. And it will take a lot of sustained effort and teamwork. And chocolate. But I'm an experienced "climber" and will take on the challenges. I have the right equipment. The weather is good. And I'll try to share- and enjoy- the climb in progress.
