I think Knightian uncertainty is a very useful concept. Sometimes "I don't know" is the right answer. I can't estimate the probabilities, I have no evidence, no decent priors -- I just do not know. It's much better to accept that than to start inventing fictional probabilities.
Black Swan isn't a theory, it's basically a correct observation that statistical models of the world are limited in many important ways and depend on many implicit and explicit assumptions (a typical assumption is the stability of the underlying process). When an assumption turns out to be wrong the model breaks, sometimes in a spectacular way.
Nassim Taleb tried to make a philosophy out of that observation. I am not particularly impressed by it.
The trouble, of course, is that "I don't know" is not an action. If "I don't know means" "don't deviate from the status quo," that can be a bad plan if the status quo is bad.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.