The primary motivation for humans is progress.
This is what author of the book Essentialism: The Disciplined Pursuit of Less, Greg McKeown, based his concept of Minimal Viable Progress (or MVP) upon.
An MVP is the minimum amount of progress you can make within a given time period. Creating an MVP for your Idea allows you to get it into a tangible form so you can have a conversation with others about it. When creating an MVP, aim for tiny wins — they are motivating!
Extra Credit: Watch this interview with Greg McKeown on the method of Essentialism to hear more about the power of progress.