What's something you assumed was common knowledge until you found out most people had no idea?

[Peter]

There's a specific, slightly disorienting feeling when you casually mention something you've always assumed everyone just knows, and the room goes quiet, or someone asks a confused follow up question that makes it clear this was not, in fact, common knowledge at all

Sometimes it's a practical life skill, sometimes it's a random piece of trivia you picked up so early you forgot it wasn't universal, sometimes it's something specific to a job or hobby you've been doing long enough that the knowledge just feels like baseline reality rather than specialized information

Curious what everyone's version of this is, the thing you mentioned once expecting a nod of agreement and instead got a room full of blank stares

[Outlaw]

Mentioned once that you should never put metal in a microwave and got asked why like it was some obscure fact rather than something I assumed literally every household knew by age ten

[Abbie22]

Found out fairly recently that a shocking number of adults don't know how to properly change a tire, assumed this was just something everyone picked up at some point and apparently not

[Joel5]

Mine is that raw honey never actually expires, mentioned this once and got genuinely argued with by someone convinced I was wrong before they looked it up themselves

[Ryan84]

Learned the hard way that most people don't know you're supposed to let meat rest after cooking it before cutting in, felt like universal kitchen knowledge until I realized how many people just don't do this

[Router53]

Mentioned that daddy longlegs aren't actually spiders technically and watched several people's entire understanding of the natural world quietly crumble in real time

[AEWCallum93]

Mine is that you shouldn't refrigerate tomatoes if you actually want them to taste good, seems like such basic kitchen wisdom and yet it surprises people constantly

[ObserverEffect68]

Mentioned once that goldfish actually have a memory span way longer than three seconds and got treated like I was making it up on the spot

[ForumGremlin]

This thread is a great reminder that common knowledge is way less common than the phrase implies, half of these replies are things I also just assumed everyone already knew

[HardyBoy_WCW]

Found out most people don't know the difference between affect and effect despite it being drilled into me so early I forgot it wasn't universally taught the same way everywhere

[Coastal Estuary]

Don't hoover any wires. After dodging every lead and cable with good amount of caution for all my life, I had the misfortune one day in a rush to go over my laptop table. It stripped the rubber casing easily and damaged the wiring. New work laptop cable later. I won't be doing that ever again

[RedBuffer]

Assumed everyone knew how to read a analog clock face quickly without thinking about it and apparently that's becoming less universal than I expected with how digital everything is now