Question

Hard Nut to Crack a problem that's very difficult to understand or solve; a difficult person

Accepted Answer

That last algebra problem was a hard nut to crack. Benjamin Franklin used this expression, which had been popular once the early 1700s. In those days people didn't buy nuts that had already been cracked out of their shells. They had to do the cracking by hand, and some nuts were tough to crack. Later, the meaning came to include any kind of complicated jam or even a person who was hard to persuade.

Idiom	Hard Nut to Crack
Example	That last algebra problem was a hard nut to crack.
Meaning	a problem that's very difficult to understand or solve; a difficult person
Origin	Benjamin Franklin used this expression, which had been popular once the early 1700s. In those days people didn't buy nuts that had already been cracked out of their shells. They had to do the cracking by hand, and some nuts were tough to crack. Later, the meaning came to include any kind of complicated jam or even a person who was hard to persuade.

Hard Nut Crack Problem Difficult Person Algebra Understand