I've been developing for 2/3rds of my life, but still had a bit of a revelation when I saw SOLID and TDD together click into place properly.

I'm not sure how to incite this revelation in other people. I had nearly a decade of people talking about dependency inversion and unit/integration/systems tests and it just kind of washed over me. If there was a way to get these interlocking concepts across to people reliably, it would revolutionise software engineering.

It might be good to just go to the source and read the GoF book.