At one of my old jobs we had this annoying offer that appeared all over the site; it was confusing, convoluted, and presented in obnoxious ways. We all (marketing folks) hated it. Every damn time we experimented with turning it off, revenue went down.
"If only users would stop clicking the damn thing and stop handing money over to us because of that click, we could finally turn it off!!"
(A bit of an oversimplification, as I know it did some damage to the brand. But the point still stands: Most marketers today live and die by testing -> measuring -> dumping money/effort into anything that catches fire. We're not going to continue using tactics that don't produce, which means that in many cases user behavior drives our decision making.)
You've got to market your product if you want people to know about it. Assuming you're a hacker/maker, just building a product and hoping people will magically find it isn't a real strategy.
You mean my side project, superawesomecrazyfuntime.heroku.com, will never make money unless I tell people about it!? How absurd, good day sir... I say good day.