WASHINGTON – Some people scoff at professional generosity.

Nice guys finish last, they jeer, and the upstart you give a boost to now probably won’t remember you when he scampers across your skull on his scurried way to the top.

Those smirking cynics haven’t heard about Jeff Kinney and Lincoln Peirce.

These two talented men were pursuing their cartooning dreams nearly two decades ago when their creative connection was sparked through handwritten – and hand-drawn – correspondence.

It was the early ’90s, and Kinney was an aspiring cartoonist at the University of Maryland, as well as a big fan of the comic strip “Big Nate,” which he read in the Washington Post. Kinney wanted advice on how to break into the business, so he wrote to several cartoonists, including Peirce, creator of the recently syndicated “Big Nate.”

Up in New Hampshire, Peirce was struck by Kinney’s outreach.

“His letter was so different from other letters,” Peirce recalls. “And not just because it was five to six pages long. Even early on, he was very talented and very ambitious.”

Instead of eyeing him warily, Peirce did the professionally generous thing: “I wrote him back.”

Kinney was thrilled: “It was a handwritten letter, which included many drawings that provided guidance on how I could improve my prospects.”

For more than two years, mentor and student exchanged handwritten and hand-drawn insights. And each time Kinney replied to Peirce, he made sure to write: “Thank you so much for the advice and help you’ve given me – and someday, I hope I can pay you back in some fashion.”

After college, Kinney tried to syndicate a cartoon he’d started at the school’s newspaper. No takers, so finally “I took a different path,” Kinney says. “Along the way, I had a number of jobs, including the one I’ve had for about 10 years as a designer and game developer for Pearson.”

At that online educational company, Kinney helped develop Poptropica.com, a virtual world for children, which launched in 2007 – and exploded. It now calls itself the most popular kids’ site on the Web, with 130 million fans.

That same year Kinney, having been discovered at a New York comics convention, debuted his book, “Diary of a Wimpy Kid.” It exploded, too. The “Wimpy Kid” series has sold in the millions, spawned book tours and a major motion picture this year.

Kinney, 39, did not forget his long-ago mentor and friend.

Out of the blue, Peirce heard from Kinney a couple of years ago.

“I was not aware of the ‘Wimpy Kid’ books,” says Peirce, noting that his children are teenagers, just missing the “Wimpy Kid’s” demographic sweet spot.

For more than 15 years, Peirce had experienced steady though not wild success. “I always considered ‘Big Nate’ a success, or I wouldn’t have kept doing it,” Peirce says. “But I still couldn’t land a major book deal.”

Kinney and his boss, Jess Brallier, “decided to dedicate ourselves to putting great content in front of kids, and I immediately thought of ‘Big Nate.’ I’ve always thought ‘Big Nate’ deserved a bigger audience, and it was exciting to think that we could bring the comic to millions of kids.”

On Valentine’s Day last year, Poptropica launched “Big Nate Island,” the interactive world of sixth-grader Nate Wright and his adventures as a “self-described genius” and “all-time record-holder for detentions in school history.”

Kids went wild.

“All I remember is that Jeff called me after the first 48 hours and said: ‘You crashed the server,’ ” Peirce recalls. “It was their biggest launch by 20 percent.”

The sudden online popularity led to Peirce’s long-sought major book deal: “Big Nate: In a Class by Himself” just spent 11 straight weeks on the New York Times best-seller list.

“I kept all his letters and pulled them out a couple of months ago,” Peirce says. He reread Kinney’s prescient words: “ ‘Thank you so much for the advice and help you’ve given me – and someday, I hope I can pay you back in some fashion.”

Translation: Nice guys can finish first.