The Top Idea in Your Mind 
A very closely related idea is that most people have a "ground state": an activity that they naturally gravitate toward when nothing else intervenes.<p>For many people, their ground state is shopping, or talking with friends, or watching tv.  Nothing wrong with any of these.<p>For some people, their ground state is aimless coding, or writing, or drifting around some community (e.g., the community of actors, or musicians, etc).  Again, nothing wrong with any of these, and they may be a useful way of learning, or having ideas.<p>But for a very small number of people their ground state is much more focused.  I've known people whose ground state is writing papers about physics or mathematics.  And it's simply unbelievable what such people can get done in a year.  (Note, mind you, that very few professional physicists or mathematicians fall into this category.)<p>I haven't founded or worked at a startup.  My observation-from-the-outside is that founders often have to take on many different tasks.  And I wonder how difficult that must make it for any of them to become a ground state task.