Getting Things Done - GTD

Do you have what it takes?
When I talk to someone who has successfully implemented GTD, I try to find out the reason that has led him to try it. It is not just curiosity. There are many people interested in productivity-related books, blogs and applications, which fail to implement any methodology or system. I want to know what differentiates the former from the latter. What does it take to succeed? Is there a secret?