It's called the Law of Unintended Consequences, and it describes what happens when someone does A expecting result B, and at the same time, C occurs. In the case of the Writers Guild of America strike, the late night talk shows went dark for a couple of months, since they didn't have writers to write jokes for them. For the past two months, it's all been reruns on late night. In the last few days, however, David Letterman's company made a separate peace with the writers and settled that part of the strike. Last night, Letterman was back with his writers in tow. Letterman's competition (Jay Leno, Conan O'Brien and Jimmy Kimmel) came back without writers.
The unintended consequence was that Letterman returned to the small screen with a beard, as did Conan O'Brien. Now, this may seem odd, but when you think about it, perhaps not. You don't normally see bearded talk show hosts because they're all clean-cut when they're hired, and if you're on television on a daily basis, you simply cannot go through the inevitable scruffy phase of beard growing during that first two or three weeks. But if you are off-screen for two months because of a writers' strike... Ah, then you can come back, fully bearded and looking wise and distinguished, without having to go through the scruffy phase on camera. A well-trimmed beard can add a sense of gravitas. But it can also be hot and itchy, and if it's much grayer than the hair on your head, it can make you look much older, which isn't necessarily a good thing.