I have seen it written down in print somewhere more eloquently (probably one of his interviews or conversations); the thing I was referring to (incorrectly) was

I have seen it written down in print somewhere more eloquently (probably one of his interviews or conversations); the thing I was referring to (incorrectly) was not an entire talk of its own, but a passing brief remark (a few seconds or a minute) during one of the “Internal Details of TeX82” lectures about the source code of the TeX program (https://www.youtube.com/watch?v=bbqY1mTwrj8&list=PL94E35692EB9D36F3&index=12 https://www.youtube.com/watch?v=bbqY1mTwrj8&list=PL94E35692E...). Sorry I don't have a more exact reference right now.