Simplicity is good, but what is it?

Rob Tannen writes an excellent article on boxes and arrows titled "Simplicity: The Distribution of Complexity".

So, given a fixed set of elements (e.g. navigation choices), there are multiple attributes of simplicity than can be addressed to varying degrees. The success or failure of a design is largely dependent on achieving the right balance among these attributes of simplicity. An infamous example of this was BMW's i-Drive controller, designed to operate a range of automotive systems from a single control. The resulting user experience was confusing and complex as BMW relied too much on mechanical simplicity (a single, clickable rotary control) at the cost of perceptual and cognitive simplicity.

It's an excellent article, go check it out.