Well, it's never smart to "self-harm" and there's no reason to do it. It's not instinctive - it's peer pressure. Why do kids do it? Because other kids do it. Nobody did that when I was a kid. So, what would I think in that situation? I'd think this girl is very insecure and easily susceptible to peer pressure. If I was a selfish guy like a teen boy, I know I'd get laid. However, as a mature man, I would be disturbed unless she was much older and these were old teenage scars. However, if any of these "self harm marks" are within the past 5 years, I will terminate my relationship at some point soon because men like stronger women who are secure in themselves. We want partners, not problems.