I don't think it's so much about the lifetime of the component, or whether it eventually fails due to faulty manufacturing or gradual wear and tear. (What the bathtub curve gets at.)

It's that if you do make parts that are identical, and you expose them to identical unanticipated circumstances, they're likely to behave identically, and fail identically.

I've seen this w/ distributed databases. I overloaded a Cassandra instance once, causing it to OOM. That node failed, but it's distributed, so another node automatically took over, ran the same query, and OOMed, and then the last guy took the query, and very quickly I had 3 dead nodes.