TAXI.com

This whole thing sounds complex, but the TLDR "quick tip" is to just throw in a 4 minor chord (as in, the minor version of the 4th chord in whatever scale you're in) for extra emotional weight. Also, you can make it a minor 6 for more resolve. I think this is how that little melody for "The Social Network" was made.

I've posted a couple of videos on the topic a few years ago after the topic got hot again thanks to Jacob Collier. Check them out if you have a few minutes.

My explanation: https://www.youtube.com/watch?v=_kiMNwqc39c&t=2s

My follow up six months later: https://www.youtube.com/watch?v=eBW5gab0_xs&t=15s

My TL;DR = It's just a neat idea, a literal theory. It has no actual basis on the acoustical physics responsible for creating real harmony.