This is pretty condescending. When someone tells you that one day they would like to run a marathon, I don’t think you automatically assume they want to quit their job and be a professional runner. No, it’s probably just an idea that they entertain with varying levels of seriousness depending on the person. Why would it be any different if someone tells you they would like to write a book? Wanting to do something and wanting to do it as a career are two different things. If I say I want to learn Spanish doesn’t mean I want to become a translator. As far as people becoming burned out on writing shortly after giving it a shot, well that’s how we find out if we like (or dislike) something, by trying it out. There are people who dream their whole life of becoming a doctor. They take every step necessary to make sure they realize this dream. They go through medical school and residency and guess what? They find out they really don’t like being a doctor. Or the flipside is people becoming exposed to something they have always turned their nose up at, only to find that they love it. Especially now, in the digital age, being a published author isn’t much of a feat. All one has to do is look at the current list of bestsellers to see you don’t have to be Joseph Conrad to be much of a “writer” to write books, much less sell them. Besides if someone’s asking you to edit their autobiography that means that they have written something, even if isn’t published.