An Outstanding Article on Systems Used for Learning

This essay, by Bret Victor, is excellent. I feel that I consistently hit roadblocks and humps the size of mountains when learning to program and I couldn’t quite figure out what I was butting against. Victor’s essay,  
http://worrydream.com/LearnableProgramming
 was not only interesting in its criticisms of current learning environments for programming, but also answered some questions I didn’t even know I had about programming. A great read!