Fact or Fiction

I'm getting a taste of what it's going to be like to have written a book that is FICTION based on a few facts. The people who know I'm writing are very concerned with how they are going to be portrayed in anything I should choose to write. I've tried to explain that while I am excited to delve into many different forms of writing, if I write a novel it will be a FICTIONAL account. They still feel the need to give me thier perspective, opinions and specific instructions on how to write. I get an ulcer thinking about what people will think when the book is published and they "cast" themselves as one of the characters.