Noise-cancelling headphones can take away dull background chatter that's far away. But in open-plan offices, usually without even so much as differentiated desks or cubicles, when the person sitting next to you decides it's cool to bring a remote controlled helicopter to work and his friends are all laughing about it with him 2 feet behind you (true story), it just doesn't help.
But even in less extreme places, where it's just normal, good-intentioned colleagues chatting about their weekend plans or something, it's still a huge disruption for me, and noise-cancelling headphones don't solve it.
Actually, I can remember one of the most insane attention triggers I had to deal with was when I actually worked in a cubicle setting and the person in the cubicle next to me had some kind of smart phone that must have doubled as a sex toy or something because when it vibrated it was insane. I could feel his phone vibrating in my forearms resting on my desk while I was typing.
That one drove me absolutely insane.
There's also a huge component of this that is just based on natural human fight vs flight reflexes.
If you have a bunch of vague, large mammals kind of walking around right behind you where you can't see them all day, it just causes anxiety. Some people (especially many extroverts) can deal with this without a problem, and it can even be comforting to them.
But for others (especially introverts) the constant triggering of the "what's that, who is walking behind me" reflex is extremely exhausting, and it gets stimulated by pretty much everything, noise, casual movement, ping pong, whatever, going on in an open plan office. The office layout in and of itself is just intrinsically unhealthy for these people.
And I fall very, very far on that spectrum towards the introverted side. It doesn't mean I'm shy (I actually love public speaking) ... what it means is that little unplanned social interactions or hints of social interactions are a huge, constant energy drain for me.
I talked to one former boss about this and his immediate reaction was something like, "Look, you are really good at getting your work done. You don't have to worry if someone's walking by and they see you've got ESPN pulled up on your monitor or something ... we know you're getting your work done."
And I'm just like, "umm ... it doesn't work that way. I don't give a shit if you see me playing Minecraft on my computer during work hours. It has nothing to do with that. It's a physiological response to the environment itself. I can't just "switch it off" because you try to assuage my anxiety."
When it comes to this introvert/extrovert spectrum, I think it truly represents a component of workplace discrimination that really damages a lot of people, but for extroverts and managers, it just never even crosses their mind that it could even be happening at all.