I have a designated Enso sketchbook next to my painting "station" and I try to do a few Zen Circles every now and then out of the paint I am mixing.
Circles themselves are very simple, though in this simplicity exists great truth and meaning. My "flavor" of Zen Circles is a little bit different than what I've traditionally seen, but the concept is the same. The idea being, a circle is painted with one stroke, in one fluid motion. If you've ever attempted to draw a circle freehand, it's fairly challenging. The act of trying is quite therapeutic for me. Zen Buddhists consider this a type of meditation, as it requires a clear mind and full concentration. Some artists hold that a Zen Circle is the graphical depiction of enlightenment itself.
Every circle is unique, and can be seen as a type of fingerprint of the artist that created it. It is not to be closely examined or analyzed, but rather viewed passively and without thinking. Only a child-like heart can truly appreciate the profound meaning that exists within a simple circle.