>Worse, many behaviors of the system don’t necessarily have a lot of conscious intent behind them (or any)

This is one of the key reasons why I’ve ingrained the “You Ain’t Gonna Need It” principle into my development philosophy. Many times I see engineers build a system that can support a dozen different use cases, but only two are used in practice. A few years down the road when several other new features have been added and the codebase needs a refactor, the extra complexity of those ten unused features become hurdles. And anyone who knows better has moved on or been reorg’d away. I’ve lost too many hours bending over backwards to support a feature that I learn much later was never used.

Note that this applies to features that increase complexity. Sometimes you can support more with less complexity through a simpler abstraction, which I’m all in favor of.