Jef, you've written plenty on the craft of writing, and also go out of your way to teach and spread your knowledge of the craft. How would you advise a person suffering from writer's block? I'm asking for a friend.
This is a complicated question, and one where a diagnosis is hazardous to give from afar, so to speak. One answer is to forget the writing for a while and do something else entirely and do not try to write for a few weeks. Sometimes then it comes back to you. Another answer is to do automatic writing or some writing exercise where you're not trying to create a full story but just do some limited task. A third possibility is to take a classic folktale and re-tell it, or to take some favorite chapter from a favorite book, re-read it, then try to rewrite it yourself from memory, which creates variation that's interesting and may spark something. But there's a whole essay on writer's block in my Wonderbook that is probably better as something to read. And also other parts of the book.