Why does one start this behavior?
It's usually on accident to begin with. A person in pain discovers something that makes the pain stop. What it is, is really pure chance. Whatever happens to happen when they also don't want to be hurting. Brain makes link. Be that self harm, food, drugs, alcohol, sex, etc. Something makes it feel better. If you've ever had a slice of cheesecake after a breakup and gotten a moment of relief, or a martini after a hard day at work, or makeup sex, or worked out your anger over an event at the gym... Then you actually do understand the process. It's most likely, though, that your pain is transient. It heals, and you put away the Haagen Daäs, or go back to running 3x a week, instead of every day.
Why not use other distractions?
. People do. There are all kinds of substitution going on for most people, because most people are smart enough to realize that their coping mechanism sucks. However... It not only has to be at the same level to truly substitute (so we aren't actually talking getting more healthy, we're talking a whole mother ball game of screwed up... Say from cutting to snorting cocaine to extreme sports to combat zones to indiscriminate sex to, to, to). Most people also usually develop a "favorite". The one that impacts their life the
least while deriving the most pain relief from it. Be it self harm, bulemia, sports, Rx's... You name it.
Is it possible to rationalize that harming oneself is never really a solution, and that permanent damage could result?
. Not really, no. In the first place, because it IS a solution. Sometimes healthy, sometimes not. Depending on how far it's being taken on the spectrum. "It" in mild form or severe form, prevents suicide. Secondly, a main reason being that we (past the age of too dumb to understand, not meant sarcastically, a 10yo or a young teen may simply not be able to put the cause and effect together, yet... Even if they know it academically) really do understand that already. It's like smokers know smoking is bad for you. And soldiers get that their job is dangerous. And doctors have patients who die. In spite of knowing, the risk is deemed worth it for the potential gain.
___________
Myself... You might not twig instantly that I'm very much into self harm. Because I discovered sports. To the point that I can -and have- been "practicing" 10+ hours a day. So my version of self harm "looks" healthy. It looks driven. It looks dedicated/ focused/ enviable.
Nope!
It's bad juju, actually. I've torn my body apart 6 ways from Sunday. Rodeo riders might have prettier xRays, but they can't match my MRIs! :D Okay. I shouldn't be smiling/joking. But that's another way I deflect pain. I push myself, and push myself, and push myself. And things tear, snap, strain, rip, pocket, swell, and on occasion actually blow up. I have walls of accolades (trophies, medals, bragging rights), and my orthopedic surgeon has boats.
There is no difference between me, and someone who cuts, or who has tattoos from head to foot (for self harm purposes, no matter how pretty). Except that I get attagirls for my self harm, while cutters get guilt&shame.
Like a cutter can use a rubber band, I can choose to run 1 mile instead of 10. If, and only if, our pain is manageable. The biggest trick isn't learning balance or moderation... It's alleviating the stupid pain to begin with.