Simple. We know it when we see it. But how to create it? To me, it’s all about the experience of effortlessness.
Does the object get in my way? Do I have to guess about how to use it, or what it’s for, or what it means? Then it’s not simple.
An object may be beautiful, have few parts, and be completely symmetric.
A perfectly round chrome sphere satisfies these. But it’s not necessarily simple. What am I supposed to do with this thing?
On the other hand, consider a door with no handle. The door can be old, the paint can be peeling, and yet I don’t have to think. I naturally push on it and move on.
You’ve heard this before: design is about how it works, not just how it looks. If your design makes something more effortless to use, then it’s getting simpler. Otherwise, you may be complicating things.