I'm now into the piano game for roundabout 1.5 years, never had any other music theory lessons before, and I learned quite a lot of music theory while learning the famous 1st movement of Beethovens moonlight sonata (Neapolitan 6th chord, I love you :) )
Anyway, as many beginners I struggled for a long time with the flat side of the circle of fifths. Now I started learning interpretations of some famous Pop Songs, namely by Phil Collins and Elton John. Many of them are in the key of of F minor, Db major or Eb major. So I got quite used to Bb , Eb, Ab and Db chords in all kind of variations and inversions.
The song that brought my attention to the question I'm going to ask is the famous pop ballade "against all odds" by Phil Collins. It starts off with a Db + Eb in the right hand over a Eb in the flat, followed by the melody going Ab, Bb, Gb and F. So technically this an Eb7sus4 chord (Eb in the bass, right hand Eb Gb Ab Bb Db).
But when transposing this intro just a half step up, so playing D+E in the right hand over E in the bass, followed by the melody going A, B, G and F# it sounds... just awful.
Why is that? Shouldn't it theoretically make no difference at all? Does it have to do with our TET piano tuning and some notes being a few cents off?
And how the heck did Phil and Elton when starting to compose famous pop songs come up that in those keys of Db, Ab, Eb (and their relative minors) and so on some gorgeous sounding chord progressions can be made?