6.14Why this tune is hard for beginners

Because they often memorize:

Fm7-B♭m7-E♭7-A♭maj7-D♭maj7...

as a chord string.

Then if one chord is forgotten, everything collapses.

Instead, memorize blocks:

Block 1

vi–ii–V–I in A♭

Block 2

predominant–V–I into C

Now you understand the route.