You end up writing about yourself, since you are a relatively fixed point in this constant interaction with the ideas and facts of the exterior world. And in this sense, the historic form closest to blogs is the diary. But with this difference: a diary is almost always a private matter. Its raw honesty, its dedication to marking life as it happens and remembering life as it was, makes it a terrestrial log. A few diaries are meant to be read by others, of course, just as correspondence could be—but usually posthumously, or as a way to compile facts for a more considered autobiographical rendering. But a blog, unlike a diary, is instantly public. It transforms this most personal and retrospective of forms into a painfully public and immediate one. It combines the confessional genre with the log form and exposes the author in a manner no author has ever been exposed before.
[Why I Blog by Andrew Sullivan, November 2008 Atlantic]
Jenny Shank writes that “Blogs are great vehicles for unedited self-expression, as are newsy Christmas letters, and even self-published nonfiction books on overly specific topics, such as the mating habits of Red-winged Blackbirds in Northern Colorado, about which I know a little.”