(as) hard / tough as nails
a tough person who is not easily affected by emotions
What is the origin of the idiom "hard as nails" and when to use it?
The origin of the phrase "hard as nails" can be traced back to the 19th century. The phrase likely emerged from the association between the physical hardness of nails. This phrase is typically used in informal contexts to describe someone's ability to withstand challenges, maintain a strong demeanor, or exhibit unwavering resolve.