While apparently an oxymoron, simplicity can be most complex.
I made the case in a previous post, Truth is Simple, that insights into natural laws and psychological phenomena can be expressed in simple terms but that what is simply expressed does not mean is easy to fully grasp or comprehend, let alone formulate.
As Nietzsche said, the fact that apparently simple and routine things are so complex to understand and unravel is a phenomenon that one may never cease to marvel at. He also wrote
"Truth is simple - isn't that just a double lie?"and
"He is a thinker - he knows how to make things simpler than they are."Philosopher Martin Heidegger for his part wrote an entire volume on the apparently self-evident and self-explanatory question of Being (Being and Time) which, as the book shows, managed to baffle the intellectual giants that were Plato and Aristotle.
It is perhaps the mark of thinkers of rank to examine and question apparently simple phenomena that most take for granted, unravelling their hidden and concealed complexity.