I’ve seen “let alone” used on Lemmy a good number of times now and, at least when I noticed it, it was always used incorrectly. It’s come to a point where I still feel like I’m being gaslit even after looking up examples, just because of the sheer amount of times I’ve seen it used outright wrong.
What I’m talking about is people switching up the first and last part. In “X, let alone Y” Y is supposed to be the more extreme case, the one that is less likely to happen, or could only happen if X also did first.
The correct usage: “That spaghetti must have been months old. I did not even open the box, let alone eat it.”
How I see it used constantly: “That spaghetti must have been months old. I did not eat it, let alone open the box.”
Other wrong usage: “Nobody checks out books anymore, let alone visits the library.”
Why does this bug me so much? I don’t know. One reason I came up with is that it’s boring. The “wrong” way the excitement always ramps down with the second sentence, so why even include it?
I am prepared to be shouted down for still somehow being incorrect about this. Do your worst. At least I’ll know I keep shifting between dimensions where “let alone” is always used differently or something.
First I’d like to clarify how I interpreted OP’s phrase: I think they meant “check out book” to specifically mean “borrow from the library”. Seems like you came to the same interpretation, but I just wanted to mention that for anyone else who might be confused reading this, because “check out” has broader usage that could just mean “look at” without any implied reference to a library,
In that context, “visiting the library” is a prerequisite of checking out a book, so it’s less extreme. You cannot possibly check out a book without first visiting the library, but you can (as you point out) visit the library without checking out books.
“Nobody visits the library” would imply that nobody checks out books, while “nobody checks out books” does not imply that nobody visits the library.
The part after “let alone” should already logically follow from the part before. If you were to break down the task into steps, it should follow the pattern of “nobody finishes step 1, let alone step 2”.
Step 1: Visit a library
Step 2: Check out a book from the library
Does that make sense?