Here's one simple rule which I hope you're following, and to which I suspect you should give more weight: If you are already aware that many apparently intelligent people disagree about an issue, hearing another person's conclusions about that issue should have little effect on your beliefs about that issue. If you hear an intelligent person disagree with a belief for which you weren't aware of intelligent disagreement, give more weight to that person's belief than your instincts suggest. I'd give more weight to your opinions if it were clear that you relied heavily on rules such as this.

I object to your advice that "if any of these reasonable-sounding principles turn out not to work, don't use them." The evidence about what works for investing is sufficiently noisy that it's dangerous for investors to think they can get anything resembling conclusive evidence about what works. I'd suggest instead advising them to "assume these rules are necessary but not sufficient for success."