Well, I most certainly don't heed that advice. My blog violates that rule in every possible way. Every post has an agenda. I like to think that I know the other side's arguments, and I usually do to some extent, but I rarely know the other side's argument as well as they do.
On the other hand, I have nothing to lose. Charlie Munger has tens of billions of dollars to lose. I should use that to my advantage. I can bet everything without really betting anything. I have nothing to lose, and potentially a great deal to gain.
99% of my assertions my be wrong. Only 1% need to be right. The cost of being wrong is absolutely nothing. In my short time as a blogger, I've already achieved more than I thought I possibly could have when I started just a few months ago. I'm getting paid to write for the most prominent blog in healthcare IT, HIStalk! I couldn't possibly ask for anything more. I've read every HIStalk post in the past 2 years. It means a lot to be part of that.
Throw yourself out there. You'll find a soft landing.