If you want to be a bad product manager, react to every customer. They’re your customers, after all, and that’s what being “focused on the customer” is about. If your customer service staff takes a complaint from one user, make sure to get that changed as soon as possible. If a prospective customer asks about some features you don’t have during the sales process, add that to the list of the next things to work on. When you hear a comment from someone who stops by your booth at a trade show about a user interface change, make sure it gets changed during the next release.
If you want to be a good product manager, understand the market. Listen to feedback from your customers and end users, but don’t blindly follow their requests. Comments are often contradictory and it’s your job to dig deeper. Who exactly is requesting these changes — are they a target customer? Why is this new feature being requested — what is the problem, need, or goal driving it? Is this problem/deficiency causing lost sales or preventing increased usage? Product managers need to answer these questions to provide context to feature requests and customer complaints.
While some customers and users will proactively provide feedback, you also need to gather information from the “silent majority” who may have different comments. All of this input needs to be evaluated alongside information about the competitive space and your long-term roadmap before deciding whether to address this feedback or not.