Customer Research for Brand New Product Launch

I feel like you wanted another question on customer research, and someone literally just dmed me an anonymous question they want me to ask on their behalf. What would be your recommendation on finding and interviewing the right kind of customers for a brand new product launch? So i don't know how your answer might change in the scenario you got to interview the people before you built the product. But it's like companies make this mistake all the time. They build a technology and they try and gr out how to slot it in. Like en you mentioned, you're trying to launch a new product. So the business already exists. How do you not know, before you build the product, who it's