Circles are building blocks of pictures, which can convey ideas, just like words are a building blocks of sentences.

A circle has a fixed level of abstraction, and representing a complex thought requires many circles. Importantly, in a complex image each individual circle doesn't convey much information, it's the composition that encodes any information.

Words have a near arbitrary level of abstraction, so that single words can convey immense collections of ideas, so much so that new words can be defined that represent the ideas that would otherwise take many words to express.