Well, it’s not actually a fundamental…It’s more of a rule of thumb. That rule is: forget what you do know. The corollary is don’t add to it.
In other words, if you’re a casual golfer, reading more articles, watching DVD’s, and otherwise adding thoughts to your swing will make you worse.
The fact that the author of the article mentions Tour Tempo as a way to forget everything is a big plus in my book!