system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we have scars on the upper arm from shots?

I mean, needle pricks are too small to have such obvious scars.
gpt
Well, when a scar happens, it's where you skin has repaired some damage. It can't quite get it just like new every time, but it does its best. It's like your body remembering some awesome fight it had.

The scar on your arm isn't your body remembering just the needle prick, it's remembering the fight *with the disease that was in the needle prick*, which was so tough that loads of tissue cells near the pin prick also had to die; and be repaired. That's also why it all swelled up so mingingly at the time.