Primarily, it's about payoff / benefit.

Imagine you're 40 years old and you've never played an instrument. You have limited ambition - you want to have fun and play a little bit around campfire. How do you start, let's say on a guitar:

1. I show you G, C, D chords and print out a simple, easily understandable chart you can take home. You now can play hundreds of songs after 30 min lesson and a few mins of practice. You can spend time playing around and slowly learning rhythm, strumming techniques and patterns, while singing to your songs and getting a feel for your instrument. A week or three later I show you E-minor and now you can play virtually every pop song made in last 20 years. [1]
If you get excited and interested, we throw in Aminor, and eventually F Major and now you know power chords and you're the master of it all. You're having fun, you're playing, you're improving, and you're having FUN. You can focus on good techniques and sounding good. When and if you want more, we can learn basic music theory and pentatonic patterns, and then one day if you're serious and ready for some pain, you can learn some staff notation.

Or!

2. I give you some books and tell you to learn notes. You download an app or six to enable you to mindlessly practices notes every day. You spend months studying by rote and can maybe play Twinkle Twinkle Little star, poorly. But it's academic because you gave up a long time before you got there as there was no FUN to be had and you have children and work and household chores and this is a poor investment of your precious, precious time.

>>How do you hope to play anything other than basic melodies if you can't read music?

I mean, it's 2021. Look around. We are SPOILED for choices when it comes to learning! There's pianote and flowkey and casio lk line and songsterr and YouTube and tablature and karaoke apps and anything and everything. It's wonderful and we should embrace that every person can learn differently and enjoy themselves! :)

FWIW, I've played Amelie on piano, Green Onions on organ, I want to Break free on synth and made some small synthwave songs entirely from scratch without reading music (but with thorough understanding of what I was playing - keys and changes and transitions and inversions) . I've recorded a cover version of White room including Rhythm and Solo, and now play bass in a 3 piece band, for fun, without needing to read music. Yes I've learned it eventually, but frankly as a 43 year old it's brought no benefit yet in the two years since I've done so.

YES if you are a pro dedicated musician interacting with others you must learn it. But I think a lot of old-school musicians forget or don't want to understand what it's like to be a casual adult player who just wants to have some fun and jam. Empathy is lacking. Just because previous generation went through some enforced painful rite of passage, doesn't mean everybody has to - let's have an actual discussion on specific customized learning path that benefits each person's goals and constraints.

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Second point, I firmly believe, especially for Hacker-News audience, is that learning staff notation too early is counter-productive. It gives enormous undeserved privilege and primacy to C major and it prevents you from making crucial connections early on. In Western 12 note equal temperament, there are 12 notes. That's it, 12 notes, repeating. You can start wherever you want and it's the same. You don't care if you start from C or Bb. There are patterns and intervals and triads and chords and things that sound good that are completely relative and you can learn SO much without staff notation messing you up. Then you do learn staff notation, and you realize it's always lying to you. The spaces on staff notation are not representative to anything in the real world. Between E and F there's one semitone; but between F and G there are two semitones, even though they are the same spacing on the staff. And if you move from the safety of C major to anything else, you are SCREEEEEWED as na adult student wanting to have fun. Notation stops any pretense of sense logic and patterns and it's a quagmire of flats and sharps you're supposed to remember as you painfully make your way through. It takes something beautiful, built on relative patterns, and jams that lovely circle into jagged square hole that's on fire. Yes, eventually, you need to learn the same stupid crippling language everybody else uses, but that's not in any way to say that the language is beautiful or practical or helpful. It's just the notation we're stuck in Western music.

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I think most importantly, a lot of people completely conflate "music theory" with "staff notation".

I've spent a long time reading "Music Theory books" which just want to teach you staff notation, which has zero explanatory powers (and I firmly believe has negative initial explanatory value). Finally, I came upon on this [2] book, which starts with "If you want to learn staff notation, awesome; we have a sibling book for that; but this is a book on music theory which is independent on any specific notation system". I read that book and every page was revelation and insight and made me a better player. Modern motivated geeky interested enthusiastic adults don't have to be stuck in the method that our grandparents taught captive 10 year olds.

I dunno, maybe it'll blow your mind, maybe you cannot see it, but I could discuss dominant 7th and minor harmonics and modes and pentatonics and intervals and triads and augmented & diminished and all that good, meaty, fun, fascinating, geeky stuff with my instructor without needing or referencing staff notation at all.

>>It's because the grand staff is centered around middle C.

That explains precisely nothing. It's not even circular, it's a rote memorized factoid thrown out instead of explanation that can be understood and discussed. The bass and treble are off by two. Two!!! If you truly cannot see that for a student, let alone for anybody, it would've been better if Piano staffs were same notes but one or two straight octaves apart, I feel you're not making an effort to see it from anybody else's eyes. My challenge is to find a practical, discussable reason two hands on same piano are off by two notes on staff that has inherent value and cannot be trivially reduced to "because 18th century grouchy Austrians said so" :)

>>It's by far one of the easiest parts of learning to play an instrument.

Well that's just wrong, but we can agree to STROOOONGLY disagree on this one :P

1: https://www.youtube.com/watch?v=oOlDewpCfZQ

2: https://www.amazon.ca/gp/product/1986061833/ref=ppx_yo_dt_b_...