This is the opening track of Currents, Tame Impala's third album and the follow-up to Lonerism. Frontman Kevin Parker told NME this song introduces a theme running through Currents of personal advancement. "'Lonerism is about always shutting out the outside world," he explained, "but chapter one of the next story, you realise that at some point there's so much force around you that to fight it just takes more energy to shut it out. There's a big undercurrent theme of transition, a transition of the self as a person. It's about giving in to forces that you can't control, even though your whole life seems to be wrong." "'Let It Happen' is like chapter one – it's track one, but it's also the first step," Parker continued. "It's about someone finding themselves in this world of chaos – they realize it, but they've always been blocking it out, they've always been stopping the outside world from coming in, like blocking their ears."

The song puts a big emphasis on groove. Kevin Parker explained to Uncut magazine: "The backbone of Tame Impala has always been a groove. I never wanted to do a song that you couldn't dance to – or groove to at least, whatever the differences between those things. I heard a few people say it was going to be more dance or club – orientated, and 'Let it Happen' is a song where I was flexing that fantasy."

According to Parker, Currents is the most pop-orientated record that Tame Impala have ever released. "I've always liked pop music," he told The Guardian. "I love what it does to my brain, and I've shut it out for a long time. The more I question myself about why I think pop is taboo, the more I realize it's not."