Hearing loss

Age is the biggest factor.

Yes, you can mistreat your ears, but age comes for us all.

I actually find that using noise blocking IEM's reduces how loudly I play music, by the way.  Of course you always have the club kid in the subway playing music so loud everyone can hear it, but for everyone else, noise blocking is the way to go. :)

They might have to rename this place Audio-Gone.

As with everything in life, moderation is key.  IMHO and IME, if you have good quality headphones and upstream components you don’t need to crank the sound as much to hear what’s going on in the music.  FWIW. 

I often witness people playing sound way louder than necessary. They just don't realize it. Headphones and earbuds on planes or in a noisy environment is a bad idea as you have to compensate for the louder than normal ambient noise. Amplified live music is a joke - always way too loud to enjoy. Even folks just sitting in front of their TVs often play the volume way louder than necessary. And when a police/ambulance/fire siren drives past, I seem to be the only one covering my ears. Gas-powered mowers/blowers without proper ear protection. I notice hearing loss causes like these everywhere. People are just oblivious to it all.