There is more to know in life than I will have time to learn. I memorize things I need often, or things I don't need often but in an emergency I will need to know them instantly - everything else I look up on need. It gives me more time to work on the things that are important to me. Unless your goal is to win a trivia contest you shouldn't memorize everything. (nothing wrong with winning a trivia contest if that is your goal, but only a few people can do it across all contests). Every one of your examples are things that I'd look up if I need to - in every context where I'd need them I'd already be using a calculator that has those built in.

Everybody should learn CPR, hopefully taking a day every year for the class turns out to be a waste of time at the end of your life but I still encourage everybody to do it. Some people need to know what e is - but it turns out I haven't needed that since I got out of school (learning to use e was in general good for learning rigorous thinking, but no need to memorize e as that value was someplace in my notes when I needed it). There are obscure things I use all the time I have memorized - but they are specific to my job or hobbies.

Looking stuff up isn’t free, which means it both costs time and frequently doesn’t happen.

Dismissing stuff as trivia doesn’t make that fundamental tradeoff go away. Do you need to know what 7 x 8 is, or the leader of China? No, but the cost of learning commonly used facts is far less than the non existent benefits of ignorance.

The key is commonly used. I don't think I have ever needed the square root of 3 in a context where I wasn't using a calculator anyway, so memorizing it would have been far more effort than looking it up (since any calculator can look this up instantly). Does it matter who the leader of China is - for some people it does, for other it is trivia not worth the bother of looking up. Back when I was getting my degree 7x8 was important to know (even if a calculator was allowed doing the math mentally was a trick I learned - most college calculus problems are selected to have easy math so if the math is hard I probably need to back up a step and fix my mistake - this trick didn't apply to other classes though), now it is mostly useful in context of proving to my 4th grader that I can do her level of math (7x8 might come up in real life, but only in contexts of a much harder problem so I'd be using a calculator anyway)

For me, the identity of the leader of China is genuinely as commonly used a fact as the lb-kg conversion rate, or that the circumference of the earth is almost exactly 4/30ths of a light-second.

Pounds is definitely not something I "regularly encounter" -- at least in the sense that I need to know more than that it is more than 100g and less than 900g. It just doesn't come up.

Perhaps different European countries are different here..

There's a big gap between needing something and benefiting from knowing something.

If a book/movie/whatever describes someone carrying a 60lb backpack is that a big deal? There's a big gap between a 6kg vs a 54kg one.

The cost of ignorance here isn't missing a question on a test, it's not getting the joke or similar in the moment thing.

I think you are overestimating the relevance of minor bits of American (or historic) culture.

We can easily work out from the context what 60lb means. The precise figure is less relevant than the rest of the scene anyway — is a soldier carrying this backpack? An injured child?

All kinds of knowledge are relevant when reading a book. Is the backpack to be carried from Warsaw to Prague? Maybe I have a greater understanding of what that entails than you, even though I'm less sure about the 60lb.

> overestimating the relevance of minor bits of American (or historic) culture.

That’s a judgement you can’t make because by your own admission you’re unaware of the subtleties involved.

That’s the core issue. It’s not that you can’t know what’s happening it’s that you’re assuming you do know what’s happening even when you’re missing significant elements and then in a fit of circular reasoning assuming because you don’t know it must not be important.

Clues embedded in a murder mystery, signs that someone was cheating, implications of fraud, etc etc all depend on concrete details you simply gloss over.

To us the 60lb is the joke. Same for 960 ounces. It stays funny pounds for pounds.

Which then ruins more serious scenes…

Ignorance simply is a net loss no matter the subject. Token for example uses both furlong and league as a means of setting the settings tone, but also to convey information.