I think this song is intentionally left unclear. She wants to tell something, but we'll never know what it is. And also his memories are fading, making everything even more obscure. And, well, mist is also insubstantial and quickly fades away.
And I think THAT's what the song is about at it's core: Reflecting about how the past fades away as the memories become unclear and things that once were very important start to cease existing.
I think this song is intentionally left unclear. She wants to tell something, but we'll never know what it is. And also his memories are fading, making everything even more obscure. And, well, mist is also insubstantial and quickly fades away. And I think THAT's what the song is about at it's core: Reflecting about how the past fades away as the memories become unclear and things that once were very important start to cease existing.