Don’t misread this. It is not insufferable, it is insuperable, and before posting this, I had no idea what it meant. And the context didn’t help me guess at the meaning. I found the word in “Wisteria Lodge”, one of The Greatest Adventures of Sherlock Holmes.

Insuperable – incapable of being passed over, overcome, or surmounted

Usage: “I have not all my facts yet, but I do not think there are any insuperable difficulties.”