Why does David Letterman have a beard? To put it more precisely: Why did Mr. Letterman, after stepping down from CBS’s “Late Show” and a 33-year career in late-night television and all but disappearing from public life, spend the past year and a half cultivating a fleecy and prodigious mound of facial hair, which, depending on your disposition, makes this 69-year-old entertainer look like either a lanky Santa Claus or an escapee from an asylum?

Did he grow these imposing bristles to keep the world at bay while he withdrew into retirement? Was it his way of saying he was no longer the man who had spent 6,000 evenings reading 4,600 Top 10 lists and interviewing 20,000 guests, and would we now please leave him alone?

Actually, Mr. Letterman explained a couple of weeks ago, “I just got tired of shaving every day, but then it became something else, and I’m not quite sure what it became.”

In his dry Midwestern delivery, tinged with a new and unaccustomed element of wistfulness, he said: “The beard is a good reminder to me that that was a different life. I’m hopeful that I will either find something else, or something else will be presented to me.”