It doesn't matter whether it was impossible to fully determine the risk - what matters is that Patrick is responsible for shouldering the risk because nothing in writing stated otherwise. And because Patrick did not fully disclose all of the information that would have made the extent of the risk "common" knowledge, it cannot fall under the "common mistake" rules that you keep coming back to.
I find it particularly telling that he repeats ceaselessly that 1% a week is "the impossible" but completely ignored the obvious point that
the MPBOR is twice that atm.
This is much like saying that paying half the LIBOR is "the impossible" in fiat. BS.