Pricing in your own coins means personal coins may not match in value behind them. One may offer a cup of coffee for 1 coin, another for 5. Simply exchanging 100 coins with each other would mean one'll get 1/5 of value from this exchange. So 1:5 exchange would be needed. But how to know that in advance?

Black in D.C. have 8 in 10 coronavirus infections—The Washington Post. (n.d.). Retrieved May 29, 2021, from https://www.washingtonpost.com/local/dc-coronavirus-blacks-vaccine/2021/05/25/1b6208da-bd6d-11eb-9c90-731aff7d9a0d_story.html

Lyons, Richard K, and Ganesh Viswanath-Natraj. ‘What Keeps Stablecoins Stable?’ Working Paper. Working Paper Series. National Bureau of Economic Research, May 2020. https://doi.org/10.3386/w27136.