People are notoriously bad at describing their actual problems. Most of the time, they will describe their perceived solutions. What's worse, even of you get to the bottom of their problem, they won't describe their procedures that they follow day by day. This is because to them it's trivial, on the level of muscle memory, but to you as an outsider it won't even occur to ask about it unless you actually see what they are doing. By just talking to people, no matter how many hours, you'll be missing a lot of context and your product will be bad.