"Listen," says a message in the Doctor's own handwriting, a message he does not remember writing.
"Listen," the most recent episode of BBC's 50-year-old sci-fi television series Doctor Who, struck many viewers as one of the program's greatest episodes ever. Acting loopier than usual for having traveled alone for some unknown time, the Doctor wonders if anyone is ever really alone. Who are you talking to when you're talking to yourself? Maybe, he speculates, you're talking to someone from a species that hides so well you never see them. Maybe you're talking to the being that hides under your bed and inspires your scariest dream.
Finally recruiting his latest traveling companion Clara Oswald to help him investigate this question - and interrupting her first date with anxious ex-soldier Rupert "Danny" Pink in the process - the Twelfth Doctor removes the safety protocols on his time machine, the TARDIS, in order to visit the night Clara had that dream during her childhood. Clara gets distracted while guiding the TARDIS, so they instead visit the farthest future and also those scary nighttime moments in the childhoods of the other characters, meaning Danny and apparently the Doctor himself rather than Clara.
The episode appealed to many viewers (and rubbed a few others the wrong way) for many reasons, including the historic scene in which we see, for the very first time, the now-ancient Doctor at an age earlier than his mid-200s. For some, the episode packed a powerful message about how to deal with fear: essentially, do not be afraid to be afraid. It's a message that can hold meaning for many - for example, those who suffer from panic disorder, which involves a vicious cycle of worrying about having panic attacks and thereby worrying oneself into having a panic attack. Are there really creatures hiding, or has the Doctor's own imagination inflicted him with fright? How much fright do we all inflict upon ourselves?
Young Rupert worries about his nightmares and about the creature he fears might be waiting under his bed, ready to grab him by the ankles. After a frightening scene in which the Doctor, Clara, and Rupert encounter either a mysterious creature or a confused child wearing a blanket over his head, the Doctor assures Danny that fear is not a bad thing: "Want to know why that's good? Let me tell you about scared. Your heart is beating so hard, I can feel it through your hands. So much blood and oxygen pumping through your brain, it's like rocket fuel. Right now, you can run faster and you can fight harder, you can jump higher than ever in your life. And you are so alert, it's like you can slow down time. What's wrong with scared? Scared is a super power. It's your super power. There is danger is this room, and guess what? It's you! You feel it?"
When they then wind up in the past on the Doctor's homeworld of Gallifrey, reaching another point in time which they should never venture but "some idiot turned the safeguards off" (as the Doctor says of himself), Clara winds up telling a crying little boy the message she heard the Doctor tell Rupert: that fear is fuel. In a bit of closed-loop causality, Clara tells the boy whose ankles she grabbed from beneath his bed (the boy who evidently will grow up to become the Doctor) the very message that she just heard the Doctor tell another little boy more than two thousand years after the Doctor himself first heard it from her. "Listen," she tells the boy. "I know you're afraid. Being afraid is all right. Because didn't anyone ever tell you? Fear is a super power. Fear can make you faster and cleverer and stronger. And one day, you're gonna come back to this barn, and on that day, you're going to be very afraid indeed. But that's okay because if you're very wise and very strong, fear doesn't have to make you cruel or cowardly. Fear can make you kind." The surprise visit into the Doctor's past is followed by a surprise callback to the most critical decision the Doctor has made in the modern Doctor Who series.
Like fear, the message cycles. The message becomes no less circular than its subject.
Listen to your fear, for it is fuel.