It's Confucious, and it goes (well, the English translation anyway): "I hear and I forget. I see and I remember. I do and I understand."
Unfortunately, it only applies entirely accurately to visual/kinesthetic learners. Still, a good rule of thumb, since the majority of people tend toward the seeing-doing style of learning.
A collection of thoughts and links from the minds of geeks
The Code that can be seen is not the true Code
I haven't found a problem yet that can't be solved by a well-placed trebuchet