> If you want to [...] play guitar for fun [...], your multiplier probably won't stop you.
Well, mine did :-D
After 3 years of practice, I could still not accurately do what a kid can do after 1 week, or someone who plays another instrument after 20 minutes.
It was time to throw in the towel and admit that there are hopeless cases and that I was one of them :-)
The worse thing is that I did not have great expectations when I started, since I don't have any interest and even dislike complex music. But I couldn't even reach my very very low expectations... By far... since 3 chords were 2 too many and the other one would never come at the right time :-D
I think most people can be decent at most things, certainly. Humans are (almost always) normally distributed, and odds are you're between 0.5 and 2 on most scales. If you want to run a 5k, or play guitar for fun, or make a website, your multiplier probably won't stop you.
But if you want to be the best, or you're choosing a goal where demand is short (astronauts, professional tubists, etc), you'd better think about your multiplier. There's a reason music schools are so viciously selective, and it's that hard work isn't going to get you a career unless you're somewhere up in that 100+ territory.
I'm pretty sure I'm down around .1 for music. I'm fairly tone deaf, my sense of rhythm is crappy, and I've never found any part of music intuitive. I've played some instruments, I don't regret it, but I'm certainly not going to go stake much of my time on being even middling-competent.
You touch on one thing that I think is a huge deal - people with big multipliers don't necessarily feel it. That top-notch musician knows they worked their ass off, but can't experience how they would have done with a worse multiplier. It's like listening to successful founders say that you should just focus on your idea and "it'll all work out in the end" - that's sample bias like no other.
I didn't get really skeptical about pure effort and growth mindset until I started working out how specific people learn. The gulfs in effort for different people on the same achievement are shocking, and this model is far better for understanding that.