Simplicity is the act of abstracting complexity. Therefore, something is simple iff the required knowledge for understanding it is the minimum needed.

The amount of context required to understand something is an indication of the complexity of the thing we are trying to understand. Lifting a cup from a table is simple. We know the required actions to do it and we don’t need to understand gravity in order to succeed in this task.

We are free, however, to unwrap this abstraction and dive into the details of what lifting a cup requires. We are free to drill into the details of gravity, objects, forces, and go as deep as we want. Each layer is in itself another abstraction that simplifies the underlying complexity of what it abstracts.