I had a basic idea of what Lisp was before getting into it some 25 years ago. It soon became obvious that, no, I actually had no idea. It's not that what I thought had been wrong, but it had no content.

I knew Lisp the way I know that that guy walking down the street is my neighbor Bob. But since I've never had a conversation with Bob, I actually have no idea who he is.

When I see Korean writing in hangeul, I know it is Korean writing, but can't read a letter of it (nor speak a word of Korean).

These examples are like knowing what Lisp is.

The thing I had not expected was how the knowledge in the Lisp world and its perspectives are very informative about a whole lot of non-Lisp!