Pen Names: How to distinguish marketing ploys from alternate personalities by the author’s subjective experience

Is a pen name merely a name that is used for privacy, or that is expected to sell better? If so, the author may give it up if and when everyone knows who they are. But the basic question is how the author thinks and feels when they write as one person or the other. And some authors have been quite candid about it: They say that when they write as the person with this name, they think and feel this way and like these things. But when they write using the other name, they’re like a different person. They say they’ve always had different sides, like Jekyll and Hyde, but in their own way.