Kin Jinwoo wants to tell his future self that "he hopes you're not worn out". He started thinking about it during the Winner;s melon radio show when it was asked what song you would want your future self to listen to.

https://twitter.com/IUteamstarcandy/status/988679433216081921/photo/1

It's rather deep considering the lyrics. Especially the line:

You don't need to recognize me, you don't need to find me but the light that doesn't go out, it shines brightly here, it will shine forever

He was so touched that he even sang the song!