In my experience, proposals are more difficult and nerve-wracking than writing the book. When I work on my book, I think about the strengths and about what I can offer to people through my writing. When I work on a proposal, it’s hard not to think about the possibility of acceptance and rejection, which is rather more stressful.
In writing, I find it crucial to hold on to my ideas as a foundation and focus first, before considering other people’s interests. But for a proposal, especially, I have to speak to someone else’s interests. It’s all well and good for me to believe that I have great ideas and that everyone could benefit from reading my book, but, realistically, the editor at a publishing house doesn’t much care about me; they care about their job and about finding books that will sell, and who knows what else? If I want that editor to do something—like read my proposal, or offer me a contract—it’s important to know what they want, because that knowledge gives me a better chance of writing something that will suit that editor.