In theory you have a lead funnel for your project. The wider end is people who might find it interesting and check it out. Narrower, closer in, are the people who might use your project regularly. Even narrower is the section of people who might pay for a thing.
You invest your time into a thing, and pay in that way. So there is at least one person, at least part of the time in the "Paying customer" category. The more compelling your product, and the more value you get from it ( As the primary user model ) the more likely others will find that they might also pay for it.
It is not wrong to build things to solve your own problems, its a quick feedback loop for your customer ( you ).
But if you want to build to make money, you might find a problem that you identify with personally among a group of motivated problem-havers, and solve that.