When something is simple but complex, in Japanese it is called kanso ( 簡素). For something to be kanso it must be almost outwardly simple yet be internally complex.
Most martial arts are this way. They are always designed to be economical yet they are layered in such a way that it makes them complex.
Human beings are the same way. When we judge people by their outward appearance, actions or speech, we run the risk of seeing them to simplistically. We are all much deeper than we appear.
Today, as we celebrate National Simplicity day, please don't forget to look a bit deeper beyond the surface. Henry David Thoreau said, “In proportion as he simplifies his life, the laws of the universe will appear less complex, and solitude will not be solitude, nor poverty poverty, nor weakness weakness.”