Used metaphorically to denote something very challenging, not literally a tough nut.

Figurative Use

'Hard' signifies complexity or resistance, not physical hardness.

Not Literally Hard

Often used with 'crack', suggesting the effort to understand or solve something.

Refers to someone who doesn't easily change their mind or give up.

Describes someone who is tough in negotiations or discussions.

Often used in competitive contexts like sports or politics.