Mark Reilley, a reader in Upper Marlboro, says he likes to watch old sitcom collections on DVD while he exercises (hey, whatever works), including the added bits of commentary and ruminations from former cast members. "I recently purchased the second season of the 'Mary Tyler Moore' show," he writes, "and pretty much everyone (Ed Asner, Valerie Harper, Gavin MacLeod -- heck even Cloris Leachman) participated in the documentary and trivia game. Everybody, that is, except Mary Tyler Moore herself. Which leads to my question: Why do celebrities who owe their fame to a particular show try to avoid and deny that same show? Why would a celebrity refuse to appear in the permanent record of his or her own popular, beloved program?"

This is actually a good question to ponder in the wake of Thanksgiving, after many adults have once again endured the slight indignities of returning home (or the set where we used to film it) and rehashing old stories about something we did two or three decades ago, and how (cute/embarrassing/tragic) it was -- which may not fit our revised, forward-looking idea of our modern selves. MTM's absence in the DVD extras may have been a mere scheduling problem, but surely she finds time to cash the royalty checks. (She doesn't seem to fear the past, or why would she have reprised her role as Laura Petrie in that goshawful update of "The Dick Van Dyke Show" last year?)

Opting out of a class reunion or family get-together is a calculated act of withholding or shunning intimacy. Even in this retro-centric era of fame, many celebs still stumble over the concept of 24/7 graciousness. It was years before the "Star Trek" crew learned to embrace its eternal fate, after which it set the gold standard of goodwill. But many other stars never learned. My first love, Lindsay Wagner, once got testy on a British talk show when asked to reminisce on the subject of "The Bionic Woman." Should I ever meet her, I'd want to dish about what it was like to French-kiss Lee Majors in 1976; she'd want to sell me one of those spongy mattresses she now hawks on infomercials. It's hard to make people forget about what you did and be interested in what you're doing at the same time.

E-mail: celebrity@washpost.com.