Good point. I think that most of my projects have an audience but reaching them is the step that I struggle with. That's why I feel that I need to reach them somehow, i.e. paid ads.

I'll try what other commenter mentioned, being part of the communities. Reply guy, provide value, and then get some trust, grow my audience and introduce my products.

If you've built 10 products and hot no-where then perhaps your strategy is a bad one.

And yes, building something then looking for customers is a bad strategy.

I strongly recommend you spend the next month finding a market. Don't start building the next product until you have made sales. If someone says "I'd pay for something that does x" then ask for a deposit. If they say "no", then keep looking.

And no, paid advertising is not the solution. That doesn't get you users (at this point). At this point you need to talk to people.