Books can be attributed to "Unknown" when the author or editor (as applicable) is not known and cannot be discovered. If at all possible, list at least one actual author or editor for a book instead of using "Unknown".
Books whose authorship is purposefully withheld should be attributed instead to Anonymous.
I found this to be very insightful. I had low expectations because I don't know much about selfcare, but it changed my perspective and will be put to good use.