I don’t trust that the infrastructure will always work.
I’ve had my cards rejected randomly. Since I travel a lot and mainly use cards abroad, I’ve had my cards rejected more times than not. It’s pretty troublesome to be stranded somewhere and unable to get a hotel or ride a train because your card was rejected.
I always keep a fat wad of cash for that reason. Also that at any time my bank could be shut down, governments or banks could decide I don’t have a right to buy something, power outages could render payments useless, or hackers could easily take down a network if they were motivated (and state-level actors have plenty of motivation now).
This is mostly my reason too. Using payments networks makes you beholden to somebody else and reliant on their systems working properly. But nobody selling you stuff gives a shit about that, if it doesn't work, it's your fault. So it's better to take responsibility and keep cash and not be stuck because of other people's problems.
Concretely, I went across town last year with my wife to try a popular counter-service restaurant. Their payment system wasn't working, and during the time I paid for and waited for my order, they turned away about 10 other people who didn't have cash to pay.
I generally just keep multiple cards from multiple providers. I have a Visa, MasterCard, and Amex, no two from the same bank. I even have a card from a foreign bank. This doesn't solve problems with local infrastructure (e.g., vendor's payment system is down), but it does solve most other issues.
I’ve had my cards rejected randomly. Since I travel a lot and mainly use cards abroad, I’ve had my cards rejected more times than not. It’s pretty troublesome to be stranded somewhere and unable to get a hotel or ride a train because your card was rejected.
I always keep a fat wad of cash for that reason. Also that at any time my bank could be shut down, governments or banks could decide I don’t have a right to buy something, power outages could render payments useless, or hackers could easily take down a network if they were motivated (and state-level actors have plenty of motivation now).