In the movie “Moneyball,” a baseball scout advises Billie Beane: “We’re all told at some point in time that we can no longer play the children’s game, we just don’t… don’t know when that’s gonna be.”

The same is true of presidential candidates — if only they listen.

The other week, I wrote that it was time for Newt Gingrich to call it quits. Each day since, his campaign has appeared more and more delusional and less and less relevant.

It’s easy to understand why Gingrich isn’t open to taking friendly advice. After all, he didn’t get where he is by being a quitter. It took a lot of chutzpah to believe Republicans could actually gain the House majority after forty years in the wilderness. It took a lot of moxie to believe he could turn around his flailing and debt-ridden campaign — after his team abandoned him en masse last year. In both instances, he defied the naysayers and did the seemingly impossible.

Over the years, Gingrich has been rewarded for his stubbornness so many times that he has probably become desensitized to reality.

But the things that make us great can also lead us to our downfall.

To be sure, there is a time to persevere. Winston Churchill said success is going form failure to failure without the loss of enthusiasm; Gingrich seems to have taken that to heart. But there are other conflicting maxims Gingrich should now turn to. For example: Always leave them wanting more.

We’ve all seen athletes — especially boxers — who fight long past their prime. It’s tragic to watch a once feared and respected man become a joke — a sideshow. And I fear that Gingrich is dangerously close to entering into that territory. That would be a real shame. Gingrich has contributed much to the cause of conservatism, and to this presidential race. But part of being great is knowing when to exit.

After finishing a distant third in Louisiana, Gingrich said he had “no incentive to get out of the race.” That’s where he’s wrong. He does have something to lose — his dignity.