Carl Falk told the story of the song during an interview with Examiner.com
: "That was originally written as two different songs: One had a really, really good verse. And the other had a really, really good chorus. So we merged those two songs together. It was actually Savan Kotecha who came up with the idea. So we just merged the two songs and turned them into one song. When we did that, everything fell into place.
We all loved the verse. It almost has a lullaby feeling to it, the way it's structured. So it just made sense to have that with a huge chorus and all of that. It felt like the perfect 'sister song' to 'What Makes You Beautiful.' It was a long process of getting there, but once we got there and the song was finished, we thought it could be even better than 'What Makes You Beautiful.' In my mind, 'One Thing' is a better song. It's my favorite out of the three songs [that I have on the Up All Night