I wonder how many motivational speakers live out their own advice. Of those who do, how many will continue to live out their advice as they raise a family? How many will continue to walk their talk into old age? Time has a way of exposing the hypocritical and the naive.
Zig Ziglar practices what he preaches. He is 82 years old and suffered a major head injury in 2007, but he continues to speak and write. His latest book explains how he lives out what he has taught for 40 years.
It should be noted that being honest and self-consistent is no indication of being right in any relevant sense. There are plenty of honest racists out there, who continue to be racist after all of their reversals (something that often reinforces their racism, in fact), and live out long, racist lives, never once challenging their racist notions.
I’d say self-consistency and sustainability are evidence of being right but not proof. As you point out, one can be self-consistent and wrong. But the tests of self-consistency and sustainability weed out many contenders, increasing the chance that those that remain are valid.
On a lighter note, I always loved this quote from Ziglar:
Money isn’t the most important thing in life, but it’s reasonably close to oxygen on the “gotta have it” scale.