[kevan]

It's counterintuitive but when you're dealing with distributed systems lots of things are: https://aws.amazon.com/builders-library/avoiding-fallback-in...

[bombcar]

Exactly - they had a fallback system that worked well enough for the testing to pass, but not well enough for the main system to operate on it.

Interestingly enough the Amazon example there is basically exactly what happened to Target.