wat. No, this is not true at all. Most successful startups work through many ideas until they already have potential customers to work with as they build. And if the idea doesn't come together and prove that is can generate revenue, people don't build it. They move on.
This idea that someone has a vision that nobody else has bought into and turn it into a startup unicorn is a rare exception to how things go. It makes a good story, but isn't how thing play out in reality 99% of the time. Don't fall into the trap of thinking the other 1% is a reasonable expectation of how your idea will go.