One of the best kept secrets of raising money is that funding is always easier when a project is already under way. ~ Robert Ringer, Action
You can paint a picture of something that will materialize or you can get to work and turn your idea into assets and reality.
The product/market fit and proof of concept are early validations of an idea that you can push towards as an entrepreneur before you ask for investments. It takes work up front, but the reward is that you removed some of the risk and uncertainty involved in guessing.
If you can turn the picture of what you want to implement into cash and cash flow, that tells the story far stronger than words and an idea will ever accomplish.