As it just turned 40, ESPN is such a sports media behemoth, it is hard to believe the most important part of its rise to dominance may have been that it snuck up on its competitors.

“They looked down on ESPN,” said Bill Rasmussen, the man who invented the company on Sept. 7, 1979.

In the 1980s, cable was sneered at by the broadcast networks. Before NBC, CBS and ABC — as it was not under common ownership with ESPN until years later — realized what ESPN was becoming, ESPN had a huge lead. They all, eventually along with Fox when it began its network in the 1990s, have been playing catch-up on the cable side ever since.

ESPN unlocked the dual revenue streams of cable subscription fees and advertising, which combined with the fact that costs were kept down by being in Bristol, Conn., allowed ESPN to have ridiculous earnings and turned it into the Yankees of sports media companies.

It was able to operate at a discount for a long time. One of the first employees was a young man named Chris Berman, who was working at a local Connecticut station when he was hired in 1979.

Since Berman didn’t require moving fees he asked for an extra $500, Rasmussen said, but ESPN held strong, so Berman had to start at $16,000 per year. Berman would later make more.

Rasmussen was cut out very early, as the big corporate investors kicked him to the curb. He made a nice amount of money, but the company is now worth, according to some estimates, $40 billion, give or take $10 billion or so. But the 86-year-old Rasmussen has no regrets.

An optimistic man who is dealing with Parkinson’s, he gave talks to ESPN employees over the last week.

He was asked by one what his reaction was when someone said no to one of his ideas. They were wrong, Rasmussen said. He would move on to the next person.

On Sunday night, prior to the Yankees-Red Sox game, Rasmussen threw out the first pitch with current ESPN president Jimmy Pitaro. Pitaro, a diehard Yankee fan, declined to wear a Red Sox shirt, instead opting for an ESPN jersey with 40 on the back.

Equal time: Mike Francesa may want to try the Costanza approach. Remember when George started doing the exact opposite of his instincts on an episode of “Seinfeld”? Francesa may be more successful with his prognostications with this method. His contradictions have been ongoing for a long time, but with @BackAftaThis chronicling everything on Twitter, it is now an art form.

The latest? On Friday, Francesa dismissed a caller who said that then-Raider Antonio Brown could be a good fit with the Patriots. With disgust, Francesa called it “ridiculous.” On Sunday, after Brown became a Pat, Francesa said it was the “logical” move.

Thumbs up: Column contributor Mark Hale, who doubles as The Post’s associate sports editor, chimes in with props for ABC sideline reporter Allison Williams. After University of Cincinnati safety Kyriq McDonald convulsed on the field, Williams quickly found the player’s mother and reported the young man had a history of seizures. McDonald ended up being OK, but it was a scary scene.

see also Giants' radio presence is taking massive hit this season Eli Manning will be his usually accessible self this season,... Candace Parker has re-signed with Turner to do NBA and college analysis. She has added a podcast, but who hasn’t? She will do it with Kristen Ledlow. … For the NFL season, ESPN New York will have Sam Darnold and Jets coach Adam Gase on its air for weekly spots, while WFAN will have Giants coach Pat Shurmur, as well as Antoine Bethea and Alec Ogletree rotating. For the Jets, Jamal Adams and Ty Montgomery will be on FAN. ESPN NY had Landon Collins last year from the Giants but has chosen not to replace him after he went to Washington. Eli Manning had been doing spots first for ESPN NY and then WFAN for years but he declined to continue with Francesa for this season.

Clicker books: A timely review from Papa Clicker if you want to better understand the firing of Dave Dombrowski by the Red Sox. “Homegrown: How the Red Sox Built a Champion from the Ground Up” by Boston Globe writer Alex Speier describes how the succession of Theo Epstein, Ben Cherington and Dombrowski built the 2018 champions. It is well-written and receives a strong 4.4 out of 5 clickers. It may need an addendum, now.

This is a doubleheader today, as Papa Clicker also reviewed Phil Knight’s autobiography “Shoe Dog,” about the rise of Nike. It received a 4.5 rating, which is just below the all-time best of 4.6, so in other words, it is highly recommended.