My power went out for 12 hours and I couldn't even buy a bottle of water.
I had $20 in my wallet but the corner store's card reader was down, and the cashier just shrugged and said they couldn't take paper money anymore, which really drove home how helpless you can be when a system fails.
That's a perfect example of how convenience can become a single point of failure. We've traded real flexibility for digital ease in so many small ways. It leaves you totally stuck when the tech glitches.