Product Management is all about understanding problems and painpoints.
It’s best to experience the problems your customers experience first hand. In most cases, this means that you worked in that domain before. For example, working in construction then transitioning to a construction startup. Here, you understand the problem your product tries to solve on a deep level because you experienced those painpoints yourself.
But experiencing these problems is not always possible. The next best thing is to talk to those that experience the problem first hand. This means talking to customers and potential customers within your target audience.
Finally, the most easily accessible (especially for large companies) but least effective method to understand the problem is to speak to those that interact with the users and customer. Think Customer Support/Success and Sales teams.