That is the most important thing because it will guide all of your research and help you pick the best concepts. If you don’t know what the user needs, find them and figure it out. You can ask them, but one of the tricky things is sometimes they don’t know what they need. If you went up to a bloke on a horse before cars existed and said “what do you need?” he’d just say a faster horse. So instead you’re looking for clues to the problem, rephrasing the problem like “this man needs to travel from A to B somehow” and leaving the how really open to creative solutions.
Your job is to understand the design needs, and pair them up with what you know about technology and engineering to deliver a solution.