تعريف ومعنى "[hang] on by {one's} fingernails"

What is the origin of the idiom "hang on by one's fingernails" and when to use it?

The origin of the idiom "hang on by one's fingernails" is not entirely clear, but it is believed to have originated in the early 20th century as a metaphorical reference to someone who is clinging to a ledge or other precarious position by their fingernails, desperately trying to avoid falling. Over time, the phrase has become a popular way to describe any situation where someone is barely managing to hold on.