From “Total Request Live” to a radio station with the “Top 9 at 9” on any given night, it’s been proven time and again: People love a good pop culture countdown. On paper it seems incredibly simple — and yet it took until Casey Kasem pioneered the concept in 1970 to take off.

News of Kasem’s death on Sunday prompted an outpouring of remembrances from fans, many of whom reminisced about listening to “American Top 40.” The Post’s Marc Fisher wrote about how Kasem brought a splintered music culture together every week with his mainstream list of popular songs. The idea gained steam, and ever since countdowns have been a mainstay of pop culture. Why is this concept so incredibly popular?

Aside from the obvious answers (countdowns are fun, music brings people together) are the psychological ones.

“The human brain is innately curious,” explains Pamela Rutledge, director of the Media Psychology Research Center. “It is hardwired to solve puzzles and find answers, so things like the countdown play right into the ‘need to know.'”

In other words, we can’t stand to not know how something is resolved — that need “triggers our primitive survival instincts,” Rutledge said. Once a countdown starts, people are naturally interested in what the order will be, or the lucky song or video that makes it to No. 1.

Another reason: People crave lists and simplification of data. While the brain desires answers, at the same time, it’s fundamentally lazy — and a countdown or list means that the heavy lifting (sorting through all the data) is already complete.

“Someone has already done all this filtering and curated the information for you,” Rutledge says. “So, we like it, because that means we have to expend less cognitive energy. It simplifies things for us. We save energy.”

Boiling down songs to lists — and incorporating music trivia in them — was what set Kasem apart from other disc jockeys; and essentially kept him from being fired. According to a Billboard profile from 1997, Kasem was working in the late 1960s at a Los Angeles radio station that had just let go two of its other on-air deejays. One day, Kasem found a magazine that had trivia about various singers. He started telling those stories when he introduced songs on air, and listeners loved it.

“In that instant, not only was his job saved, but the engaging formula behind what would become ‘American Top 40’ was born,” the article read.

Sure enough, when he pitched the idea of counting down songs and weaving fun facts into each number, it became hugely popular. And even when music fragmented in the early 1990s, he was able to split the countdowns into separate shows for each genres. Then the concept became even bigger.

The list gimmick paid off big time, as people enjoyed the concept of supplementing songs with more information. “He may as well be one of a kind because he has always been such a stickler for details,” said radio personality Wink Martindale in the Billboard story. “Casey went to great pains to never give a false fact. As a result, he really made a niche for himself, which made him famous. He really is America’s records-keeper.”

Cultivating music into the countdown format not only speaks to the fact that people like organization, but the very idea that this is *one* list that many people enjoy appeals to our sense of social identity.

“When we see lots of people liking something — presumption here, being a song — we pay attention and try to figure out if we like it,” Rutledge said. “It’s defining a social norm: ‘This is what the tribe likes, and I want to be part of the tribe.'”

That doesn’t mean that everyone has to enjoy the No. 1 song at the end of a countdown: “It’s not that we have to like it,” she added. “But it defines more than popular music. It’s a cultural statement.”