I mean, where does my book leave off and my blog begin, or maybe where does my blog leave off and my book begin? I'm spending a lot of time with the book but the blog comes up once a day and I'm seamless. Sort of.
I'm trying to keep me separate and not steal my own thunder, but it's hard. I'm me, after all, and I can only spread myself so thin. I think I finished the book (again) today, that is, the rewrite of the first draft. The danger with rewrites is that if you use material from the first or later drafts as you go along, you are in dreadful danger of repeating yourself and not noticing. It happened in only one of my books, that I am aware of. By the time you, and your editor, and your copy editor, have read it so many times, you can't remember where you last read some of the deathless prose, so that the same paragraph may show up twice in the same draft. Horrors!
So you can see the dangers inherent in writing a daily blog. More repetition, for one thing. But also coming up with an idea in the blog that I decide I'd like to use for the book. I read something and I think, "Gee, I wish I'd said that," and I have. Is it okay to plagiarize one's own writing?
I hope so.