On the PCT I wasn't able to come up with an 8th Principle. Then again, I wasn't really trying too hard to think about it.

To be a Principle, it ought to be essential to follow. In other words, before submitting an idea, ask yourself: "Can I get the most out of life without following this Principle?"
If the answer is YES, then it's not a Principle having the same stature as the other seven.
If the answer is NO, then ask yourself if the concept is already covered in one of the seven Principles. If none of the seven Principles cover it, then please post the idea and we'll debate it!
I also promise to debate it in my brain while I yo-yo the CDT!
I hope to come up with an answer by the end of the CDT!