Some people pratice self-mutilation to relief their depression. 20 something years ago I frequented a girl who was full of scars under her clothes, she was pretty good at finding plausible excuses for the scars (plausible to a 20yr old ignorant about that practice), one day she confessed that she did this to herself and that she was unable to stop... It's not a memory I tought I would revisit but your question made me think of her and her dangerous mania.

It's a hyperbole.

Injuries generally cause brain to release endorphins, which in turn releases dopamine, causing addiction. For example, cutting is a common type of self-mutilation depressed people do. High-intensity exercise arguably also does the same thing - as your body is "microinjured" by strain, your brain releases endorphins to help with the pain, causing effects like "the runner's high".

Maybe they should have said something along the line "replaces the pain with a new one and gives you adrenalin that surpresses it and is addictive"

"There are more things in Heaven and Earth, Horatio, than are dreamt of in your philosophy."

And the Internet is the place where you get exposed to them at random.

Is this a useful first aid technique?

Like for Aron Ralston, who was trapped under a rock and had to cut off his own leg to escape: would it have reduced his pain if he had stabbed himself in the shoulder to the bone?

Would this best be done with, say possibly, acupuncture needles or an ice pick, so as to minimize the damage and to maximize the relief?

Gunsmoke TV episode:

Doc: Well, Billy, we'll have to amputate your lower left leg - it's shot plumb thru with gangrene.

Billy: Will it hurt, Doc?

Doc: Hell yeah, it'll hurt! But thanks to Hacker News we have a new pain treatment: every time you yell. Chester here will stab your right leg to the bone with this h'yar ice pick. And Mary will hold a leather strap in your mouth so your teeth don't crack off! Don't forget to breathe.

Billy: I'm obliged and grateful to be part of your research program, Doc, but can't you instead just wait 10 minutes while I drink this here quart of whiskey and pass out? Then you can do as you wish.

Doc: Hell, no, time's a'wasting! Hold him down, fellas! Doctorin' progresses only a step at a time!

+1! wtf!