Some amount of hiding state makes APIs easier to use though. Keeping data structures coherent, for example, means you need to only interact with them through th

Some amount of hiding state makes APIs easier to use though. Keeping data structures coherent, for example, means you need to only interact with them through the provided interfaces. This also means that you could internally change the data structures (eg. from deque to ring buffer) and not expose the implementation details to the outside world, causing downstream breakages. What you describe makes sense for small components built by a small, tightly knit and highly skilled team. The issue is that at some point the software grows enough that you can't hold the whole thing in your head at once, or you need to make it reusable to external developers.