Currently, most of the flow of value is from fiat currency (USD,CAD…) to crypto-currency (USDT,USDC…).
This allows the providers of so called ‘stable’ coins (Tether,Circle…) to promise1:1 exchange rate.
However the promise is not a guarantee of 1:1 exchange rate - when going back to from ‘stable coins’ to fiat currency. To find why please check -
The danger in the stable coins (thought experiments and the real price of Bitcoin)