A lot of people assume the Earth, Wind & Fire song "September" singles out September 21 because it marks the changing of seasons.

That's wrong, according to lyricist Allee Willis.

Willis said they picked that date just because it sounded the best.

There's no deeper significance.

It's the 21st of September, which means it's time to listen to the Earth, Wind & Fire song over and over and over again.

But do you remember why the band singled out the 21st as the date for the song? Many people wrongly assume it has something to do with the seasons changing — September 21 is the first day of fall — but it doesn't.

Allee Willis, who co-wrote the song with the band, told NPR in 2014 that they just picked it out because it sounded the best.

"We went through all the dates: 'Do you remember the first, the second, the third, the fourth ... ' and the one that just felt the best was the 21st," Willis said.

Willis said it's a question people ask him a lot.

"I constantly have people coming up to me and they get so excited to know what the significance was. And there is no significance beyond it just sang better than any of the other dates," she said. "So... sorry!"

Willis, who was a struggling songwriter in 1978 when he was asked by Earth, Wind & Fire to write their next album, also said he initially objected to the "ba-dee ya" refrain in the lyrics. He tried to get Maurice White, the band's lead singer and songwriter, to change it.

"I just said, 'What the f--- does 'ba-dee-ya' mean?' And he essentially said, 'Who the f--- cares?'" she said. "I learned my greatest lesson ever in songwriting from him, which was never let the lyric get in the way of the groove."