[armoredkitten]

Yes, the pain scale is subjective, because, well, any attempt to communicate internal feelings and experiences is subjective (by definition). But subjective metrics are still useful as a way to try to achieve a shared understanding. "It hurts, but it doesn't hurt as much as other things I've felt before" is still informative, even if it's imperfect.

And the pain scale is useful when you are talking to someone who is not used to talking about their internal feelings -- some people aren't as expressive as others. And some people have less of a grasp on the language you are communicating in. I would expect if I were a doctor or nurse, I wouldn't want to base my standard of care on how capable my patient is of finding an appropriate adjective to describe how they feel.