system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why doesn't scar tissue heal?

I've read how after five years have passed you are a completely different person on the atomic scale. The atoms that comprise your being are, apparently, completely different. Yet your scars and injuries remain: why is that? Has the DNA information to reproduce the original structure been lost and all that remains is the information for propagating the wounds?
gpt
Your skin is composed of several layers.  The very bottom layer (stratum basale) contains the epidermal stem cells which divide and grow to form new skin cells.  If you get a shallow cut above this layer, the stem cells are able to patch up the area and your skin will heal without a scar.  If the cut is deep and goes below this layer, a different cell type patches up the damage.  This cell type is called a fibroblast.  Fibroblasts are more concerned about fixing the damage than they are about how it looks, so they lay down fibrous tissue and seal up the wound.  

Think of it like trying to fix a hole in your boat.  If the damage is kind of small, maybe you'll use a sealant and try to patch it up nicely.  If however there's water rushing into the boat, you grab a roll of duct tape and get to work without thinking twice about what the boat will look like.