I also have a friend who struggled to apply it. The problem with him is that he struggled to be consistent with most of the habits he was trying to build. Once one masters the art of being consistent or just the simple habit of "showing up," that's when everything truly sticks and starts to fall into place.
Another thing, it mostly starts with getting rid of your old "bad" habits.
Ilmatarian t1_j23lull wrote
Essentialism from Greg McKeown. Like Marie Kondo but for your whole life and without the dubious „spark“.
By the way, I read Atomic habits and was less successful in applying it to my own life.