Fiat is tricky for travellers...
Today I had artist's block. So here is a recent true story.
It's not hard to get scammed when you are a jetlagged traveller.
I know someone who received a two-tone Egyptian pound coin instead of the 10 Thai baht coin for change from an airport restaurant in Phuket. They are a similar size, weight and look so unless you are already familiar with the local currency, it's a small scale scam when substituted.
1 Egyptian pound = 1.78 Thai baht (so you can do the math)
It's not easy to buy a coffee whilst in transit at a Chinese airport KFC, if you are not in possession of renminbi (RMB/CNY), or a Chinese payment app (e.g. Alipay or WeChat Pay?). ALL OF THE CHINESE PEOPLE PAY WITH THEIR SMARTPHONES.
VISA not accepted. And obviously, not Bitcoin (in any form).
So a very tired traveller/husband might have to trudge down to the ground floor foreign exchange with passport in hand to pay some high fees to procure local cash.
Mental math is handy for shopping/bargaining at markets.
20 Thai baht = 0.83 Canadian dollars
20 baht and 20 CAD are both green bills but have very different values!
There were many moments during this trip of imagining how much easier it would be to eventually have a global unit of account and medium of exchange.