Banish talk like "I don't know anything about that".

In I don't know, Eliezer isn't arguing that you shouldn't say it, but that you shouldn't think it:

what you say is another issue, especially when speaking to nonrationalists, and then it is well to bear in mind that words don't have fixed meanings; the meaning of the sounds that issue from your lips is whatever occurs in the mind of the listener. If they're going to misinterpret something then you shouldn't say it to them no matter what the words mean inside your own head

"I don't know" is a good way to duck when you say it to someone who doesn't know about probability distributions. If they thought I was certain, or that my statement implied actual knowledge of the tree then the statement would mislead them.