I tried this out once a few years ago. I'd been reading a short story where a number of characters were in a strange nightmare-world, having to face their worst fears, and I thought I'd try it out myself by incubating the worst nightmare my subconscious could conceive of. I fell asleep ready to face whatever monsters, extreme environments, and other challenges it would throw at me-- and what resulted was the most boring dream in my entire dream journal. Boring, boring, boring. I woke up twice while it was going on, but when I fell back asleep I just ended up back in the same boring dream, working alone in a hot place where nothing ever seemed to get done. A while later, I realized I might have learned something rather significant....