When something is impossible, the average human has enough intelligence to realize how stupid it would be to attempt such a thing.

Let's use an example to make this a bit more concrete.

It's common knowledge that flapping your arms and jumping off of a tall building won't result – ever – in suddenly taking off and flying.

No, the inevitable conclusion of immediately plummeting to the ground is frightfully obvious to any sane person.

You could ask anyone on the street:

"Do you think it's a good idea, to jump off a tall building flapping your arms?"

To which the response would be probably some variation of:

"What the fuck is wrong with you?"

Let's humor the argument for a moment, and follow this hypothetical dialogue:

"No, seriously, I'm just trying to figure something out."

"There's nothing to figure out. What a moronic question. Are you on drugs?"

So, I suppose that might be the only exception. If our subject was on some serious dose of psychedelics, then maybe…

"Yeah, actually. I just took a few hits of LSD."

"Acid? Really? How… retro I guess… Hmm. Okay, but… You're not driving, are you?"

"No, I don't have a license."

"That's not what I asked."

"That's fair. No. I'm not driving."

"Okay. A few hits of LSD?"

"Well…"

"What?"

"Okay, it was more than a few hits."

"Oh, God. How much more."

"Like a sheet…"

"Jesus."

"…or two…"

It's at this point that the average person might face-palm.

But then it would dawn on them:

"Uh, what's your name?"

Oh, shit.

"The narrator didn't give me one."

Fuck. Right. Let's call our subject Frank.

"Oh wait, they just did. My name's Frank."

"Nice to fucking meet you, Frank. I'm–"

Dammit. Ted.

"–Ted, apparently."

"Okay, Ted, and where is this tall building, anyway?"

Fine. They're both sitting at an outdoor cafe, at separate tables, in downtown New York. Manhattan. Lots of tall buildings, plenty of opportunities to try to fly.

"Frank, you're the one who asked ME if I thought it was a good idea to jump off a tall building flapping my fucking arms."

Right.

"Okay, you're right Ted, I guess those LSDs made me forget my point of view for a moment. But you never answered my question."

"That's correct, because anyone - even a moron - knows that if you try to jump off a fucking tall building all you end up doing is painting the fucking sidewalk red."

Geez. Who wrote these characters.

"But I think I can fly, Ted."

"Listen buddy… to be frank…"

"I'm Frank. You're Ted, remember?"

Cute. But Ted continues:

"If I were you - like if I was Frank… and if I thought, I really truly fucking believed that I could fly… then acid or no acid, I wouldn't take such a leap as my first attempt."

"You wouldn't?"

"Hell no. Look at these fucking skyscrapers."

He gestures casually around him at the towering buildings.

Frank nods.

"So why wouldn't start by trying to take off from the fucking ground first, buddy?"