[nulltype]

The inner workings may be obscure, but I really like it when the outer workings are not. I use the Google Datastore (although Postgres would work here too), which I'm sure is super complicated internally. Externally though, it has certain properties that form a fairly simple mental model.

With that mental model, you can predict from reading some code what the possible error cases or race conditions could be, or what the state of the datastore entity would be after running some code against it. Perhaps that's not precisely "Software Complexity", but "Library Complexity" instead.

I was going to use Redis as an example, but the internal workings are probably too easy to understand.