system
Given the following post, respond as if you're commenting on Reddit:
human
LI5: Why can't everyone just use a common currency?

I got full marks in both AP Macro- and AP Microeconomics, so explain like I'm 5, but know the basics!

**EDIT: [SOLVED], thanks everyone, I feel really stupid :P**
gpt
Currencies are influenced by economics. By using our own currency, we make sure we're not being dragged down by countries that are poorer than us.

Example: The richer countries in the EU aren't too happy with what's happening in Greece because the Euro is suffering from it. Or rephrased: How their strong Euro is influenced by the weak Greek economy.