external vs. internal motivators

In our class on Monday, one of the points brought up was that external motivators overpower internatl motivators to the point of elimination. This topic is particularly interesting to me because I have watched my brother struggle with this problem. He never had an especially strong sense of self-motivation. Parents and adults offered things to trigger an inspiration in him. They tried punishing and threatening him. They even tried to open him up to out-of-the ordinary things to see if anything would spark in him. My mom will never give up her quest to inspire something in my brother, but now that he is in college, he's finally getting a chance to explore interests on his own. What do you know- he is doing better than he ever has. No one watches over his shoulder making sure he completes assignments or treats him as if hoping for the wonder we all know he is capable of. The pressure is off and he is discovering a world of which he was previously oblivious.
This is, however, only one example. Many kids have people and pressure pulling them in every which direction, and they depend on things such as grades to keep them focused on school. Internal motivators stretch farther than imaginable for external motivators, but external motivators are required for some participants to meet the minimum non-inspired work.