This is a nice article, but the title strays into 'Fox and the Grapes' territory. Exactly-once delivery is pretty much always what you want -- in contexts where

This is a nice article, but the title strays into 'Fox and the Grapes' territory. Exactly-once delivery is pretty much always what you want -- in contexts where all manner of delivery guarantees are possible, from Java's concurrent queues to Go's channels, pretty much everyone delivers a message precisely once. Of course, you can't always get what you want, and in a distributed system exactly-once delivery is not possible in general. But in the cases where it is possible, it's often worthwhile: it's just a whole lot easier to reason about than a system where messages can be arbitrarily re-delivered.