The phrase hard nut to crack is an idiom that describes something or someone that is difficult to deal with, understand, or solve. It originates from the literal difficulty of cracking open certain types of nuts, like walnuts, which have tough shells.When used figuratively, it can refer to:A problem or situation that is challenging to resolve.A person who is difficult to understand, convince, or get to know.For example:This math problem is a hard nut to crack.He’s a hard nut to crack; he rarely talks about his feelings.Person A:Hey, how’s your new project going?Person B:Honestly, it's been tough. This client is like a hard-to-crack walnut.Person A:Really? What’s making it so difficult?Person B:They’re very specific, but don’t communicate clearly. Every time I think I’ve got it figured out, they change something.Person A:Sounds frustrating! But you’re great at solving tough problems. I’m sure you’ll crack it soon!Person B:Thanks, I hope so. This one’s just taking a little extra effort.