The Most Important Idea in Computer Science from Alan Kay

Alan Kay has got to be one of the smartest people alive. I wish he wrote more. My favorites are his answer to the question "What do you believe is true, even though you cannot prove it?":

http://www.edge.org/q2005/q05_8.html#kay

and his essay "Predicting the Future":

http://www.ecotopia.com/webpress/futures.htm

His other work is quite impressive, also, but these two are by far my favorites.

One idea that Kay has championed is what he called somewhere "recursive design", in which you begin with a kernel that is both simple and universal and then build the rest of a complex system in terms of that. The relation to Lisp is obvious, and Lisp and Smalltalk environments are probably the best examples of systems designed this way. I'm curious what other examples people here might cite.

First .coop site I've come across.