I think Sandi has done a superb job of explaining the difference between quiet power and submissive behaviors. I have nothing to add here as Sandi's captured many of the essential points that you might want to pay attention to and absorb into every cell within your body.
Give it some time and eventually you'll get the hang of it.
First and foremost, you must STOP being afraid of W and her reactions. Be absolutely fearless with your own brand of quiet power that is assertive without being aggressive.
