Less vs fewer is definitely a mistake made more by native speakers, who may have known the words most of their lives without a defined meaning until later.
This grammar mistake is one of my pet peeves with online chat, and really seems to be getting worse in the last few years.
it’s not a mistake because it’s not a real rule
This isn’t an example of how modern English is going to the dogs. Less has been used this way for well over a thousand years—nearly as long as there’s been a written English language. But for more than 200 years almost every usage writer and English teacher has declared such use to be wrong. The received rule seems to have originated with the critic Robert Baker, who expressed it not as a law but as a matter of personal preference. Somewhere along the way—it’s not clear how—his preference was generalized and elevated to an absolute, inviolable rule.
one less thing for you to worry about
Weird Al is not a fan either, if his song Word Crimes is any indication.
It’s “less” or it’s “fewer”
Like people who were
Never raised in a sewer
I hate these word crimes
Like I could care less
That means you do care
At least a little
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