In his newest post Anthony Ferrara looks at some of the things he calls the foundations of object-oriented design, as set of three things (and principles) to keep in mind when working on OOP applications.
It's quite easy to mix up terminology and talk about making "easy" systems and "simple" ones. But in reality, they are completely different measures, and how we design and architect systems will depend strongly on our goals. By differentiating Simple from Easy, Complex from Hard, we can start to talk about the tradeoffs that designs can give us. And we can then start making better designs.
He starts with the "simple vs easy" concept and how sometimes making the two meet can be difficult. He includes an example of interdependent interfaces and how they add complexity (and, in turn, make them less easy to use). He also talks about accidental versus essential complexity and how, sometimes, "accidental" isn't always a bad thing. Finally, he wraps it up with a few principles to remember in your development including recommendations to reduce (accidental) complexity and keeping the target developers in mind, making it easiest for them to use.