Both of the sibling comments, plus good nibs don't have any rough edges which touch the paper. They've been ground/sanded down so smooth that they effectively hydroplane on the ink they're depositing.

You can improve some inexpensive nibs by simply "writing" on a high grit sandpaper or sharpening stone, but if the metal is too soft you can quickly wear away the writing surface entirely. I'd do this with the pilot disposable fountain pens with good results.