Let’s take a look at them under the cut….(Unless, of course, you’d prefer to follow their advice.)
“Curiosity killed the cat”
Oh, what dastardly things curiosities are, especially to the cats that they kill—or rather, what dastardly things cares are. “Curiosity killed the cat” originated from Ben Jonson’s 1598 play Every Man in His Humour, wherein one character exclaims:
"Helter skelter, hang sorrow, care'll kill a Cat, up-tails all, and a Louse for the Hangman."
This use of care comes from Old English, in which the noun means sorrowful or anxious. Therefore, this original form of the idiom warns that sorrow and worry--not curiosity--will mentally and physically wear on those whom they plague. Both sorrow and worry cause stress, and that stress is (according to Jonson) powerful enough to wear out--even kill--cats, who are known for their ability to get themselves out of tight, sometimes dangerous, jams.
Care also served as the root word of carful, an Old English adjective that can mean careful, anxious...or curious.
Fast forward three hundred years to 1898 and the publication of Brewster’s Dictionary of Phrase and Fable. This dictionary defined the idiom (then still in its original form) as:
"Care killed the Cat. It is said that a cat has nine lives, but care would wear them all out."
It is unknown when curiosity “officially” replaced care, but the earliest traceable instance of the idiom’s current form can be found in a periodical run by The Galveston Daily Record in 1898 (the same year as the publication of Brewster’s Dictionary):
"It is said that once 'curiosity killed a Thomas cat.'"
No record detailing the reason behind the switch from care to curiosity exists, but most likely the answer lies in the Old English adjective carful, the negative connotation of curiosity (i.e., “sticking your nose where it doesn’t belong”), and the inquisitive nature of cats.
But in any case, with curiosity now taking residence in care’s place, the idiom’s meaning has changed to warn of the dangers to which following one’s curiosity might lead.
An example from Tomb Raider:
“I wonder what this does…” said Lara as she reached out to grasp a lever embedded in a nearby section of the temple’s wall. She was just about to pull it when Professor Von Croy slapped her hand away.
“I told you not to touch anything!” he snapped. “These ruins are old, and they are filled with any number of traps that could injure or kill us both! What is the expression that you English have? Oh, yes: curiosity killed the cat. You would do well to remember that, child.”
“Ignorance is bliss”
Fans of the Matrix might remember this idiom from Cypher and Agent Smith’s dinner exchange in the first film. Fans of eighteenth-century English poetry might also remember it from the end of Thomas Gray’s “Ode on a Distant Prospect of Eton College”:
Since sorrow never comes too late,
And happiness too swiftly flies.
Thought would destroy their paradise.
No more; where ignorance is bliss,
'Tis folly to be wise.
In this poem (from which the idiom originates), Gray laments the happiness of his childhood, which ended when he became an adult and in turn learned the suffering of the world. He muses how wonderful it was to be—pardon me—blissfully ignorant of said suffering and pities the children who, though carefree now, will also one day learn of it. Thus, the idiom “ignorance is bliss” means that, sometimes, it is better to remain ignorant of a possible misfortune and not worry about it than to learn of it and worry about it.
Another example from Tomb Raider:
"So, are you going to look at any of these records of your father's, ah, 'other quests'...?" came Alister's voice through Lara's ear piece.
"No," she replied as she glanced around the hidden office full of files detailing her father's unsavory dealings. "He loved my mother, and whatever he did, he did it to find her." Setting the torch on nearest stack of files, she stepped back and watched as the entire room caught fire. "That's how I'll remember him."
"Sometimes ignorance is bliss," said Zip through the ear piece.
The idiom has also inspired a wave of commonly known put-downs used to insult the intelligence of the person to whom the speaker is talking or those around the speaker: "If ignorance is bliss, then you must be orgasmic!", "...you must be the happiest person alive!", "...why aren't there more happy people?", etc.
Will curiosity really kill the cat? Is ignorance truly bliss? Well, I guess that depends on what you want to discover and how badly you want to discover it. Knowledge is the key to power, and power is the key to change, but as Peter Parker's uncle Ben once so famously said, "With great power comes great responsibility." Whether or not you should pursue a particular piece of knowledge can be a tricky decision to make: foresight is impossible to gauge because you don't know what you'll discover (if you discover anything at all); if you do discover something, you have to decide what to do with it; and if discovering this something has consequences, you have to accept them.
So how about it? Are you willing to accept the possible consequences of biting down on that apple, Eve? Is presenting fire to Humankind worth your liver, Prometheus?
If you decided to click on the cut despite these idioms' warnings, I figure you already have your answer.
Old English Made Easy