This is a very, very good post.
It may be a little long, but it is enlightening. Well worth the effort reading it through and bearing some bits and pieces in mind.
Essentially, the reason why we have such a difficult time knowing what we don't know is because of survivorship bias. This means we only get information from the survivors, not those who perished and vanished from the records.
This was recently covered by ZeroHedge as well.
In it, we also learn from one of Donald Rumsfeld's utterances:
There are known knowns; there are things we know that we know.
There are known unknowns; that is to say, there are things that we now know we don't know.
But there are also unknown unknowns – there are things we do not know we don’t know.
I love being mind-fucked like that.
Even more so when it teaches me not to learn so much from the success of others, rather to learn more from the failures of others.