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?”
Thats where patterns repeat. It’s just for convenience, an 8th note is an 8th note no matter the signature but its how you count the beats. If a piece is in 3/4 the phrases will feel different from 4/4. So, if youre sight reading, it makes it easier to predict when phrases begin and end, when to come in off rests, etc.
I hope that helps somehow lol.
Also helpful to know where it’s appropriate to take a breath on a wind instrument if it’s not marked.