If you cannot identify the customer, how do you know the product is something they need? The recipe for success seems to be to understand a market or vertical

If you cannot identify the customer, how do you know the product is something they need? The recipe for success seems to be to understand a market or vertical and then offer a solution to an existing problem (their greatest pain) that particular market faces. By targeting a market instead of a solution, you can cultivate your customer list, and up-sell or cross-sell relevant, related solutions. The other almost-guaranteed path to success seems to be to create an internal tool for your own business pain, and offer that solution to others that are experiencing the same problem. But trying to sell a product that you have not validated is an uphill battle.