At first I thought this was on becoming a professional author, now after I read it I understand this is on how to maintain professional author as a career. One

At first I thought this was on becoming a professional author, now after I read it I understand this is on how to maintain professional author as a career. One thing I'm curious about though- the author in question never brings up cover designers or editors, but does advise to listen to the agent and ask a lot of questions. I do know that cover design can be controversial and that editors can often encourage changes that make the author feel like garbage (eg. 'change the entire tense of the novel' or 'kill this beautifully written scene'). What is the advisement for that?