Janus, the personification of thresholds, beginnings, and endings, has had many depictions over the centuries. Common to them all and distinguishing him from every other occupant in the pantheon of Roman deities were his two faces opposite each other on either side of his head. He looked both ways with his two faces, and this, the Romans thought, made him the perfect god to preside over the boundary between any two given situations: war and peace, earth and heaven, past and future. He was the doorkeeper, the boundary master.
One conspicuous difference you’ll notice among Janus’ many depictions is that in some, his two faces are identical, and his head a perfectly symmetrical mirror image; while in others, his two faces are markedly different, one side bearded while the other side is not, or one side visibly aged while the other side is youthful.
In A Charlie Brown Christmas, Charlie Brown is depressed. He doesn’t feel very uplifted by the approach of Christmas, ostensibly because it has gotten “commercialized,” but really, as he admits to himself early in the special, because he perceives that nobody likes him, so, “Why do we have to have a holiday season to emphasize it?” Charlie Brown’s self-derision is healed in the end by the kindness and closeness of his friends. But many more people besides Charlie Brown struggle at Christmastime, either because they also think that nobody likes them, or else because the memory of lost loved ones becomes more painful now, or else because the changes they’re seeing all around them—the increased crowds and clamor; the repellent false sentimentality and self-interestedness of actual commercialization; the growing darkness, both spiritual and literal—just puts extra stress on them.