It depends. If you’re writing a PhD dissertation, you’re probably not writing it for fun or to make money—you’re doing it to get a degree and advance your career. 

That means you have to know what you’re doing, and that means going into the process with your eyes wide open. It’s not just about getting a good grade at the end of your PhD program; it’s about getting a good grade in an area that really interests you and making yourself an asset to your field. 

That said, if the topic is something that interests you but isn’t something that’s challenging or interesting—or if it doesn’t challenge or interest you enough—then this might not be the right choice for you.