If you listen to James Bay's - Let it Go, it sounds sad yet written in major key. In general, not just for this song, what in theory makes this happen?
I've read people suggesting flat majors make a subtle difference but after transposing the song to another major (c-major) in hooktheory, https://www.hooktheory.com/theorytab/view/james-bay/let-it-go, I find it still has some sadness to it.
Could you please explain how this is done? How does someone make this choice? Is it in the melody, chords, or a combination of the two? Chord progression?