These Common Sayings Don't Really Mean What Everyone Thinks They Mean
English is a strange language, and that has a lot to do with the way it evolves so fast that its evolution very often gets away from its community of speakers. No one is in control of language: Even the venerable Oxford English Dictionary was forced to admit that the word "literally" didn't mean, y'know, literally literally. In fact, the OED decreed, it was acceptable to use "literally" to mean "figuratively"—its opposite meaning—because it had entered common usage that way. As Senior OED Editor Fiona MacPherson told BBC Radio 5, "If enough people use a word in a particular way... it will find its way into the dictionary."
Literally as was the case with "literally," some phrases entered common usage and persist to this day—but have taken on the opposite meaning to its original. In many cases, it had to do with forgetting the origins and context of the phrases.
Here are a few curious examples of these phrases that don't really mean what everyone thinks they mean. Knowing the truth doesn't just allow you to be that guy at the next meeting (because no one will invite you to parties ever again); some of the original phrases make for good food for thought. Literally.
Remember that scene in Die Hard when Hans Gruber whispered "Curiosity killed the cat" to John McClane as he shot him in the knee? No? That's because it didn't happen. But it's the kind of thing that movie villains are wont to say as a warning against poking around too much.
The original saying was "Care killed the cat," back when "care" was a synonym for "worry." You can see this in literature, as early as the 16th century—the playwright Ben Jonson used the phrase in his 1598 play Every Man in His Humour. Shakespeare himself used it in Much Ado About Nothing, where Claudio says "What, courage man! what though care killed a cat, thou hast mettle enough in thee to kill care."
The original phrase was therefore an admonition not to worry about the future too much. And when the saying did evolve to become "Curiosity killed the cat," it was often answered by a second part: "...but satisfaction brought it back." Meaning that the proverbial cat might waste one of its lives letting its curiosity get the best of it, but satisfying that curiosity is just as powerful.
Remember when Jesus said "The left hand shouldn't know what the right hand is doing"? No? Well, you should, because He actually said that— it's in the Bible. Jesus was referring to the act of giving alms, which He preached shouldn't be done for glory. Acts of charity shouldn't be broadcast to the world; they should be done because they're the right thing to do. God will be the only witness, and from God will come the only reward. So, when you say of someone that his left hand doesn't know what the right is doing, it's actually a very good thing.
Okay, this one's up in the air. Proponents of the common usage of the saying point to the fact that an equivalent saying exists in German (Blut ist dicker als Wasser), which dates back to the 12th century. However, there are those who argue that the original complete phrase was "The blood of the covenant is thicker than the water of the womb": which meant that persons who make a promise between them share an even deeper bond than those of family—the very opposite of what we take it to mean.
Now this is something everybody's bigoted, ultra-rightwing uncle might say as he screamingly insists that every bit of criticism against the government is treason. The complete phrase comes from American Senator Carl Schurz, who said, "My country, right or wrong; if right, to be kept right; and if wrong, to be set right." Instead of preaching blind obedience to the country, he meant to say that true patriotism is to help correct the course of a country that was going astray.
This phrase—commonly shortened to "bootstrapping"—is meant to congratulate self-made men who use whatever resources they have to get started on the road to success. This is, in fact, where the term "booting" a computer comes from, because a computer's startup process is exactly the kind of self-contained process that the phrase is meant to conjure up.
But here's an easy way to illustrate its original meaning: Try to pull yourself up by your shoelaces or bootstraps. Now that didn't go to well, did it? That's what the phrase originally meant to imply—a futile attempt, not a successful one.
Popularized by Robin Williams' character in Dead Poets Society, "Carpe Diem" is probably the most oft-quoted Latin phrase in modern history. The actual quote comes from the Roman poet Horace, who wrote, "Carpe diem, quam minimum credula postero"—which translates to: "Pluck the day, trust little in the future." What the saying meant was to do as much as one could today, not because one shouldn't think of the future, but precisely because one must plan for it.
Interestingly, Horace was also a follower of the philosopher Epicurus—himself the victim of the changing whims of language, as "epicurean" is now taken to describe someone with lavish, gourmet tastes. In fact, while it is true that Epicurus spoke about pleasure being the greatest good, he also preached about keeping one's pleasures very simple, so as not to fall into the trap of overabundance.