Behold the advantage of VisaNet and friends. When you swipe on these networks, your authorization is handled in a dedicated bunker on some of the best silicon we know how to create (Telum). The network links between issuers and acquirers are monitored in real time by humans who will contact ISPs and NOCs at 3am local time if need be.

This is why the apparently extortionate merchant fees. Precisely so that when you do swipe it always works no matter what. I genuinely cannot recall a single instance where I was unable to obtain payment auth in a grocery store using Visa or Amex.