No, no, no. I could write an entire essay on why this is poor advice. George Costanza from Seinfeld found a niche, but could never break from that type. Dickens wrote a whole bunch of different stuff, including sports sketches as The Boz, satire, social commentary, newspaper and magazine articles. If you're in finance, and want to concentrate on finance that's different, but I'm talking about being an artistic writer. Even those who write about finance need to find hooks and creative ways to make it interesting and understandable to the common reader.