Songfacts®:

• Lissie started writing "Best Days" back in 2015 when she was working on her My Wild West album, but could never quite finish it. The following year, she brought the fledgling song to her songwriting friends Daniel Tashen and Ian Fitchuk in Nashville and they helped her to complete it.
• The song finds Lissie both looking back at her life to date and also looking ahead optimistically to the future: She explained to The Independent:
  
  "Simply put, I was reflecting on what we strive towards as 'adults' and then perhaps upon getting those things, just trying to maintain and stay safe. And for myself, [there's] this almost aggressive hopefulness that my future is bright: trying to find some peace with the surprises that life throws us and how I and we have no idea what incredible adventures await.
  
  As I've lived with the song, other layers have surfaced for me. One is all the possible versions of reality that exist in parallel layers simultaneously and all the possible future versions of myself there could be, and the idea that maybe when we look back on the 'good old days', in our present we are living in the 'good old days'. But on the surface [the song] is about having hope for the future. I also like how universal this song feels for me: it's about my own life, but think it applies to anyone at any stage of their life."
• Lissie reworked this as a piano ballad on her 2019 album, When I'm Alone: The Piano Retrospective.