The power of a life that backs up one's words is beyond dispute.
Barring that, there is the power of being open about one's scars that have come by not doing/living right, and about what one is doing/has done to overcome.
But usually, we are some combination of success and failure. So we can stive to exhibit both. That too is powerful.
The person who does not exhibit these--a life that backs up one's words and/or openess about one's scars and what one is doing/has done about them--will certainly suffer their effectiveness in correlative measure.
"Do what I say, not what I do" just does not have as a big of an impact.
This is just the ins and outs of "moral authority," and a taking of human nature into account in it.
My main concern is the path most physicians must take to becoming a physician works strongly against them living a healthy lifestyle. That is a tough, tough issue, where I think fundamental change needs to occur.
That's my take.