The below sentence is from one of a self-help book by IAN TUHOVSKY
Wouldn’t you have your own problems and your own life to worry about? Yeah, that’s right. People don’t even remember. They don’t care.They couldn’t care less.
He already mentioned "They don't care" then why it is followed by the sentence "They couldn't care less" which also has the same meaning "They don't care"?
Is this some kind of emphasis? or that is redundant? or is my understanding incorrect?
And my mind says the second sentence exactly means "They don't care at all" but the first sentence is just "They don't care". But I don't find any difference in these sentences, both looks same to me.