Simple is not the opposite of complex, but rather, signals singularity and harmony within an object.
An egg and an apple. Both are complex organic constructions, however, they are understood as simple as every aspect of their presence is synchronized in one practical purpose.
A loaf of bread and a cotton tee shirt, a heavy spoon, a glass of water.
In his books, Haruki Murakami often describes characters eating a "simple meal," which will comprise of a steamed vegetable and some fish. What is simple is often clean and clear.