People understand that actors play parts. Whether you think of acting as “pretending” or whether you subscribe to method-acting notions of empathetically channeling some part of your own personality, everyone understands, or should, that the character and the actor are two different people. I have never met Jack McBrayer, but I doubt he’s exactly like Kenneth the Page on “30 Rock.”

We have all heard stories about actors specializing in easy-going heroes who turned out to be ambitious or misogynistic jerks in real life, or about great horror villains who, in real life, are adored by their friends and love to play bridge and make tiramisu.

I think we also admit that a similar dichotomy is possible for people who play “themselves,” whether as radio personalities or talk show hosts or observational comedians. Even in these cases, the private personality might be different in some ways from the public persona — and we’re usually OK with that, as long as we aren’t slapped in the face by it. But sometimes the gap between the persona and the personality is too jarring to get over.

The climax of one of my all-time favorite movies, “A Face In The Crowd,” comes when the populist good ol’ boy Lonesome Rhodes (Andy Griffith) is suddenly revealed to TV viewers as a vicious man with contempt for his audience.

One possible inspiration for “A Face In The Crowd,” at least in small part, was Arthur Godfrey. I remember Arthur Godfrey from his waning days, as a guest on other people’s TV shows and as a commercial pitchman. But in his prime, the early 1950s, he was arguably the most popular person on the brand-new medium of TV. Like Regis Philbin at the height of “Who Wants To Be A Millionaire,” Godfrey had simultaneous success in daytime and prime time. He had a 90-minute daily program and two weekly prime time shows.

Godfrey could be funny, but he wasn’t really a comedian. He could sing and play the ukulele, but he wouldn’t have been a success on musical talent alone. His success was based on his personality: warm, relaxed and friendly. His rich voice and laid-back delivery made him sound like your favorite uncle.

In 1953, one of the regular performers on Godfrey’s prime time shows was a singer named Julius LaRosa. Somehow, LaRosa got on Godfrey’s bad side. The stated reason was that LaRosa missed a dance lesson which Godfrey had ordered for the entire cast. LaRosa said this was due to a family emergency. Some have claimed that Godfrey was jealous of LaRosa’s growing popularity.

Whatever happened, LaRosa performed a song one October night on the live prime time show. Afterward, Godfrey announced to the audience that this was LaRosa’s swan song and that he, LaRosa, was leaving the Godfrey program for bigger and better things.

This was a shock to everyone, including and especially Julius LaRosa. In fact, LaRosa — an immigrant — didn’t understand the term “swan song,” and had trouble comprehending at the time that he had just been fired in front of millions of viewers.

The viewing audience had no way of knowing the backstory of this on the night of the show, but it came out soon enough in the press. LaRosa held a press conference to explain that his live, on-the-air firing was completely unexpected. Godfrey held a press conference to say that LaRosa had lost his “humility.”

Godfrey would fire others in the coming weeks.

Today, almost to the point of cliché, historians point to LaRosa’s on-air firing as the turning point in Godfrey’s career. Godfrey remained on the air, but his image was never the same after that and his popularity declined. People couldn’t quite reconcile the nice-guy image with the possibility, proven or not, that Godfrey might be a not-so-nice guy in real life. Was that fair? Who knows. But it’s what happened.

After my annoyance last night, I did not watch tonight’s “Jay Leno Show.” But I understand that he’s fighting back against the criticisms of him by Conan O’Brien and others.

Jay Leno will, no doubt, thrive on his return to “The Tonight Show.” But I wonder if this tempest in a teapot, and his sometimes-petty reactions to it, has damaged his nice-guy image in a way that will play out over time. There have been other comedians delivering their own pointed commentary, of course, some of it mean-spirited. But the squabble seems to have taken Jay further away than anyone else from his normal public persona.

Maybe this won’t have any long-term impact; after all, David Letterman seems so far to have survived revelations about his own private life that were in contrast to his TV persona. (Dave’s not out of the woods yet, since his matter could still play out in court, risking additional accusations and counter-accusations.)

Still, I wonder if someday Conan O’Brien will be thought of as Jay’s Julius LaRosa.