Boredom is the key.
The amateur seeks new, change and exciting. The moment a project loses these traits, the amateur gets bored and seeks another project.
The professional thrives in boredom. She embraces the repetitive nature of showing up day after day working on supposedly the same thing knowing that even though she can't see it yet, progress is still being made.
It's one thing to have a bright idea. It's another to make it see the light of the day. That requires us to embrace boredom.