Baek Ah Yeon described what the song is about, "'Bittersweet' expresses the wishy-washy emotions caused by one making a bittersweet promise and then breaking it the next." She added, "If I were in a similar situation I would patiently wait, and give the person up to three chances."
In regards to "Just Friends", which J.Y. Park participated in writing the lyrics, the singer mentioned, "He was attracted to the intricate scenario presented in the lyrics and enjoyed working on the project. He said that he liked the song."