For me it’s time signatures in music. I grew up playing instruments, played in several orchestras, etc. But no matter how many times someone tries to explain time signatures to me, it makes no sense. I don’t understand why people place such importance on it. To me, notes have a pitch and a duration, maybe some dynamics. That’s it. I don’t understand why people try to needlessly complicate it. It doesn’t give you anything.
My wife will hear a song and go “Oh neat, it’s in 5/8.” And I’m like “How tf do you know that, and why does it matter?”
One thing this reminded me of is Bootsy Collins explaining funk. How when you’re playing bass you put the root on the one. https://youtu.be/H2MMuNkCLZY
The time signature is about emphasis, and there are common ones. I’ve bolded and italicized big and small emphases on the beat numbers.
Common time: 1 2 3 4 , 1 2 3 4 ,… example peter gunn theme
Cut time: 1 2, 1 2, … example stars and stripes forever
Waltz: 1 2 3, 1 2 3, … example the blue danube
6/8: 1 2 3 4 5 6, 1 2 3 4 5 6,… example the wreck of the edmund fitzgerald
5/4: 1 2 3 4 5, 1 2 3 4 5,… example Mission Impossible theme
Some time signatures are very similar, like waltz and 6/8, the difference is where the emphasis is placed. Waltz has just one big, emphasis placed on the one, where 6/8 is also groups of three, but has a big emphasis on the 1 and a smaller emphasis on the 4th beat. An alternate way to count in 6/8 time is 1 2 3, 2 2 3; 1 2 3, 2 2 3;… which emphasizes how 6/8 time feels like two groupings of three, within one bar, with the biggest emphasis on the one.
This is the basic version – composers will play with expectations and add their own accents on top, etc., so you won’t always hear the emphasis as I described. Reasonable people might even disagree about whether a piece of music is better described by one time signature or another, because they can be so similar.
I was in band growing up and i also couldn’t explain time signatures even though i was able to read music and play them; it is something you learn without necessarily being able to verbalize, since it is about how the music feels, based on subtle emphasis.