Legend has it that, following the tragic events on November 22, 1963, Daniel Patrick Moynihan resurrected a quote favored by the young Irish president who’d just been gunned down in Dallas.

“What’s the use of being Irish if you don’t know the world is going to break your heart one day?”

Well, that one day is now nearly 50 years ago. It has been almost 50 years since Lee Harvey Oswald settled into his sniper’s nest on the sixth floor of the Texas Book Depository and got off three shots, killing President John F. Kennedy. 

That weekend, the nation was transfixed. First by the televised funeral, then by the subsequent shooting of Oswald himself, by Jack Ruby. 

It was sobering and shocking. The nation mourned, then slowly moved on.

Or maybe not.

The assassination remains a national obsession. Last week, the brilliant AMC cable drama “Mad Men” completed its third season. The show depicts the New York advertising world of the early 1960s, a world in which woman, Jews and Catholics are viewed with a mix of suspicion and hostility. 

As this season drew to close, the life of the show’s main character Don Draper (Jon Hamm) was falling apart. His wife was growing sick and tired of his lying and cheating.

Then came Dallas. November 22, 1963. Clearly, the show’s creators were linking the public tragedy of JFK’s assassination with the private tragedy of the crumbling Draper marriage. It was fine television.

The problem is that TV shows and movie makers and book writers have been hauling out the events of November 1963 for, well, five decades now. Countless books, movies and other stories are set during the JFK assassination to suggest that in some way “everything changed” after those events.

“Mad Men” joins the not so noble ranks of tepid films such as Michelle Pfeiffer’s 1992 movie “Love Field,” and Joyce Carol Oates’ overwrought novel “Because it Is Bitter and Because it Is My Heart.”

There are two problems here. First is the mere fact of quantity. 

In and of itself, “Mad Men’s” use of the JFK assassination as a backdrop was effective. But this is something we’ve seen far too often. 

Similarly, in any story set in the early 1960s which depicts a character (usually female) who is changing, the character usually goes off to “volunteer for Kennedy.” (See Ellen Barkin in “This Boy’s Life,” among others.)

The other thing is the notion that “everything changed” after November 22, 1963. Now, it is true that monumental upheaval followed as the 1960s wore on. 

Still, are we somehow to believe things would have really been different had Oswald’s rifle not worked properly? Change was in the air regardless of what happened in Dallas. Change is always in the air. For better or worse.

Then there’s the other problem. My assumption that Oswald was the only shooter. Because if TV and movie writers are not creating some somber scene with the JFK assassination in the backdrop, then it is the conspiracy industry which continues to pick over the events of November 1963.

Did you know that last week the Associated Press and other serious news organizations reported the findings of a Dartmouth -- Dartmouth, for heavens sake! –- scientist who found that the famous photo of Oswald holding a rifle and a Marxist newspaper could not have been faked. 

Almost 50 years later and a scientist at a prestigious university is analyzing a single photo which, according to Kennedy conspiracy buffs, was created by the government to make Oswald look evil.

Well, that settles that!

The granddaddy of all conspiracy narratives, of course, is Oliver Stone’s 1993 film “JFK.” The movie is brilliant, yet preposterous. 

Still, you would think throwing nearly all of the JFK conspiracy theories into one three hour movie would at least leave everyone exhausted. But no.

Coming up this week on the Discovery Channel, two new documentaries: “Did the Mob Kill JFK,” as well as “JFK: The Ruby Connection.”

With all due respect, it might be time to take a breather from all of this. Clearly this was a moment of national trauma. But there have been other such moments. 

Kennedy was neither saint nor sinner. He was a little of both. The Irish, and so many others, had their hearts broken that day. But that’s happened before as well.

And we can move on from that. Can’t we?