What’s up with that? The conventional answer is, “The brain can’t process a negative.” But if the brain can’t process a negative, phrases that contain a negative (like “the brain can’t process a negative”) can’t be processed by the brain. But they can. The brain understands perfectly well what “don’t think about a blue elephant” means. The task is clear. The cause of the failure is somewhere else.
Language and the Imagination
The issue is that, to understand what someone is saying, your unconscious mind, you imagination, puts the words together into things it understands, out of its library of remembered and imagined things—events, images, sounds, thoughts, sensations, and so on. That means that, to know what you’re not supposed to think about, your mind has to understand what the words “blue elephant” mean, which is quite hard to do unless you imagine elephant and color it blue. By which time, of course, it’s too late!