I'm not a writer, but I do write, and I also read this advice when younger then promptly ignored it. I think it was from Bukowski.

It sounded, and still sounds, like "Only run if running bursts from the soles of your feet and you feel like you'll go crazy if you don't." Well, no. It might be good advice for a professional athlete -- I wouldn't know -- but you can run whenever you damn well feel like it as an amateur. So too for writing.