I was watching this YouTube talk as I'm interested in exploring Smalltalk for a bit due to recent HN discussions. some people mentioned it was the greatest productive language ever. Others said it wasn't. But what I did get to understand is that it is unique. Also, Alan Kay is not an unknown name on these forums and he's a fun writer to read. So I figured, why not watch a Smalltalk lecture?
I'm just about 7 min. to this video and what I saw at 7:43 blew my mind. I timestamped the video so that you can get some of the relevant context. It reminds me a lot of Brett Victor's Learnable programming blog post  that has been frequently mentioned on here.