If your users are also your customers, then you are lucky. It makes a lot of design and marketing decisions a lot simpler. You can focus laser-like on providing features that your users are willing to pay for.
However the user is not always the customer. For example, if you are selling software to a large enterprise then the person making the buying decision is not the user, which is why so much software used internally in large companies is so crappy.
And many of you working in the consumer Internet space have the same business model that broadcast television has had for more than half a century: give the service for free to users and get money from advertisers. To be successful you need to simultaneously keep your users (consumers) happy while keeping your customers (advertisers) willing to pay you. This is often hard.