Where do we get the idea to eat or have sex? Maybe we don't. As Pinker argues, we're not a blank slate. Perhaps the impulse to engage in self-injury when under extreme emotional distress is also inborn.
We are starting to understand the havoc stress wreaks on the body. We are also starting to understand the strong endogenous physiological calming effect self-injury prompts. Perhaps the ancient Chinese acupuncturists have understood the positive effects of small non-impulsive doses of self-injury on the body for ages.
I wonder if self-injury acts almost like an inoculation - when given a small amount of manageable physical adversity, the body's soothing and contentment system is able to overcompensate and fortify itself. Maybe the body intuitively knows to default to self-injury under periods of stress because there are dramatic and sudden decrease anxiety due to increases in endogenous calming agents, being that stress is particularly harmful to the body. [There's something about stress triggering autoimmune diseases here that should be looked at. Perhaps it isn't a coincidence that Benadryl can be used both as an antianxiety as well as an antihistamine.]
After all, humans are not the only animals that engage in self-injury. My first research project (cited in TIME here) mentions that a certain percentage of people report getting the idea to engage in self-injury from an outside source; however, the other side of that is that some people report never having learned the idea from anyone. Perhaps it is, in fact, an inborn impulse we have that is defaulted to in times of stress because it is protective to the body against stress. This is not to say, of course, that some people don't get the idea to cut from other people. Surely this must be the case. But what about the people who spontaneously start cutting without outside influence? How can that be explained?
I'm beginning to think that the impulse to hurt oneself is a hardwired fail-safe.