system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is Entropy and why can't it be decreased?
gpt
Ok imagine you have made a sandcastle. It's perfect, it has turrets and windows and looks fucking awesome. But the wind is strong and eventually your sandcastle that you've spent ages building gets blown into the wind. Well that is entropy. 

You start off with something really ordered and neat (the sandcastle) and the wind comes along and makes your lovely neat castle into a disorganised pile of sand again. So if you imagine the start of the universe it was in it's most highly ordered state (the sandcastle) then ever since that point time (the wind) has come along to make it more disorganised. 

As to why it can't be decreased. Well that's a bit more of a tricky explanation. But essentially. Everything in the universe uses energy, and then re emits that energy. But the energy it puts out is less organised than the one it put in. If it didn't and the energy stayed just as organised. We wouldn't exist.