Am I missing something when it comes to noise-cancelling headphones?

When people suggest I use them, I feel so confused. I'm not trying to drown out noise with other noise. I'm trying to find quiet. But, am I understanding correctly that when people suggest these, they're not actually suggesting something that will give me the quiet I want? That they're actually just giving me a way to create my own noise that would be ostensibly better than the other noise?