What do we mean when we say it today?
Any fans of 10 Things I Hate About You or Nick Lowe will know that "cruel to be kind" is the name of a hit song. But this has also become a popular character or trope on TV and in the movies, too.
All the time we see a guy being really mean to some young girl only to push her to work harder and be better. Or an older woman being upfront and blunt with young talent so they know they might not make it, or will have to work way harder than they thought to get there.
We might call this figure Alex on Grey's Anatomy, Proteus in The Uncanny X-Men comics, Mother Gothel in Tangled (or so she claims), Snape in Harry Potter, or even Spock in Star Trek.
We also use this phrase in everyday conversation. If someone says he had to be "cruel to be kind" then he's is trying to be like one of these characters. It's all about telling someone how it really is to help him or her in the long run. But we'll warn you: sometimes people are just plain cruel. They may hide behind this phrase, but there's nothing kind about it.