White people may think this is new, but it's not only old, it's knowledge found around the world. A lot of tribal cultures have practiced tattooing and/or scarification. On the one hand, it shows strength, that you can survive a bunch of little injuries. On the other, it makes people stronger. These two beliefs are found in almost every culture that is really into bodymods. There are weirder versions too. The Mayans were hardcore self-injury fans. Logically that would have a similar effect.
... and now I'm wondering if people who self-injure as a coping skill get that effect. I'm quite certain nobody would have studied that. Talk about career suicide.