“What should we build?” implies that you—as my client— perceive that there is problem that your business can solve.
Without user research, this quest would be a high stakes gamble. You’d be investing time and money in an assumption that might be shaped by bias and or power centers in your company. Or, you might miss essential details about who has such a problem and what drives their perceptions and actions.
The role of user research is to lower your risk and increase your odds of success, and generate a few new opportunities you hadn’t seen before.
Too much development takes place in a vacuum. This is true in established companies and within startups. "Everyone needs a ___” is a great place to start, but it is incredibly worthwhile to gain a deeper, more strategic understanding of the audience. You are not your users.
The goal and purpose of generative research like this is to better understand which problem you should be solving... for whom... and why it makes sense for you to solve it.
Methods we use to do this include ethnography (out in the field, observing habits), interviews in context of daily life, or perhaps a diary study (asking people to record activities and thoughts over time).