Al Kipone schreef op 25 apr 2019 om 15:28:
as we know, there are known knowns;
there are things we know we know.
We also know there are known unknowns;
that is to say we know there are some things we do not know.
But there are also unknown unknowns
the ones we don't know we don't know
And if one looks throughout the history, it is the latter category that tend to be the difficult ones.