'When she was a college student, aspiring writer Carren Strock’s English professor told her, ''Some people are writers, and some people aren’t. You are not a writer.''She didn’t pick up a pen for more than fifteen years… until Robert Redford came to town.Appearing in Redford’s movie led to writing for national magazines, and then to selling her first nonfiction book to a major New York publisher.Now Carren Strock lays out her improbable journey from ''not a writer'