DDD is about deriving everything from the business side, we need to architect our products in a way that most helps achieving business success. But we cannot do it without considering the end users, the different personas whom we deliver value for. We really need to make sure who these people are exactly (if it is people), what are the issues they are facing every day and what is their goal with using our product. Once we learn all this about our users we can confidently go forward to build up our backlog knowing that all the stories in there are strategically important.