In hindsight it is always easy to say "If only I had validated my assumptions before building." But this neglects the fact that you must know the right question

In hindsight it is always easy to say "If only I had validated my assumptions before building." But this neglects the fact that you must know the right question to ask and the right hypotheses to validate in the first place. Doing customer interviews without clear objectives is a waste of time. I have found that you often come across thyour hypotheses while building the product, not from before-the-fact customer interviews. Building forces you to consider the design space of your product, and raises specific questions that you can later ask your customers about. So, let's not forget the overall goal of customer validation: Learning. If you believe that you can learn more about the market and customer needs by spending a couple of days/weeks building a product before doing the next round of interviews then do that. Of course, neither building nor interviewing work in isolation. They are a continuous loop. Interviewing without building is only useful for very initial marketing research. Similarly, building without feedback can lead you down a rabbit hole. So, how do you decide what to do next? Building or collecting feedback? Do what gives you the most learning for the time spent. If you are a developer and can build things really quickly, it's probably a good idea to do that. If you are non-technical then customer interviews may give your more learning for less time spent.