In J. R. R. Tolkien’s The Lord of the Rings, Gandalf, after talking to himself aloud in the presence of others, defends the practice as, “a habit of the old,” to speak to the wisest person available.

If you’ve never experienced clinical depression, it is hard to understand what it is like. Well-intentioned people will say things like, “just think positive,” or “just snap out of it.” Though they ...