Creating Passionate Users: The best user manuals EVER
In other words, he knew that the levels –key achievement milestones with clear rewards–are more motivating than just, "here you go... keep going." In the Parelli system, the physical reward is nothing more than a paper certificate and piece of colored string. But the mental and emotional reward is enough to keep people sticking with it and–paying more money for additional training materials (including, sometimes, live courses).
Source: headrush.typepad.com