IU revealed the back story behind her song 'Voicemail'!
She recorded an episode for MBC Music's 'Picnic', where she not only put on an emotional concert, but also poured out sincere stories to her audience. One of the songs she talked about was her own song "Voicemail", which came from her friend's story and her own story from school.

She said, "This is a story I'm revealing for the first time on broadcast. But 'Voicemail' is from my experience, and all the lyrics are from my own experience. It's a song I made about one-sided love and being rejected, so every time I sing about it, I get sad. Since you are all talking honestly about your secret stories, I feel like I'm revealing my own secret story."

After the broadcast, she said, "It's a broadcast where I was able to talk about a feeling I never have discussed on broadcast before. I feel like I got healed."

Source: billboard