system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:If I were to sell my pounds £100 to Dollars $120, the Dollar increased in value to $150, then I sold back to pounds, where has that money I've earned come from?

Currently trading is a zero-sum game- where does the cash generated come from?
gpt
It comes from the amount of investment and total wealth that a currency represents. 

If you trade pounds for dollars, and then the pound collapses, then more people will want dollars(because they aren't losing value). This increase in demand makes the dollar worth more compared to the pound. At the same time, the pound is losing value, so it is worth less as well.

The total amount of wealth in the world stays the same(in this example), but one currency becomes worth more and another worth less, making it seem like the dollar gained value when it really just took value from somewhere else. 

When there are many currencies in play, like there are in the world today, any currency can affect the market as a whole. So if the rupee collapses and lots of indian people rush to get american dollars, then the dollar goes up in value from the increased demand, your pound stayed the same value, but you still see that difference when you exchange pounds for dollars.