What is it that sparks creation? Why do people create what they do?

When it comes to the aspect of Videography and Photography, I am chasing the thought process, the turning of the gears, the story behind the storyteller. When it all comes full circle, the creator is satisfied. It's important to know, that there was something that triggered the process of a blank canvas on their screen... to go to some form of masterpiece. I'm trying to dig deep, and find that trigger and the story behind what it produces.