This accords with the philosophy Henderson's mentor George Sheehan, who wrote:
" We must have a healthy distrust and a healthy cynicism for the experts, and for authority in general. Each of us is an experiment of one. Each is an expert in the self, a witness of a personal truth, our own best authority."
I think that this is the most the profound truth about running. It does not mean that other people cannot help - of course they can; one must learn from somewhere. It means that everything must be filtered through our experience and on every run we are testing how our body is reacting. We have to learn to trust our own senses.
A simple example. There are many runners who believe, quite logically, in specialisation i.e. that the way to improve at running is to concentrate solely on running, because other activities do not develop muscles in quite the same way. These people are likely to knock out prodigious weekly mileages. Whilst other people like to mix up activities and training because they find too much of one thing is either a bit boring or over stresses the body. These people thrive on variety and will do fewer miles. Both sets of people are right.
In the same essay he also says
"My advice to these advisors would be. "Do not tell me what to do, tell me what you do. Do not tell me what is good for me, tell me what is good for you. If, at the same time you reveal the you in me, if you become a mirror to my inner self, then you have made a listener and a friend."
It seems to me that is exactly what happens on the Runners World forum and all the personal blogs. People are sharing what works or does not work for them - things that can be tested on our own little Bunsen burners. We all might be pursuing individual experiments but we are also part of a community that shares a common endeavour.
Reason N0. 9 for running: It teaches you to trust your own senses