This is a common theme around many documentaries. The filmmakers set out with a certain subject in mind, then circumstances change, which causes them to discover what the real project is. Their original subject may have been a trivial, or even bad idea, but without taking action on it, they would have never discovered what their film was really supposed to be.
Don’t worry too much about starting the right project. Start A project. Circumstances have a way of guiding us to the right one. The question is, will we listen and find the courage to adapt when your project shows you what it’s really supposed to be?