Etymology of 靜 is made up of two words: 青's extended meaning is for saying someone performed better than his/her teacher. 争 means to dispute, fight, contend, strive. But 靜 itself means calm, quiet, peaceful, tranquil. It also represents "no mind" and stillness, both critical to elite combat.
The Circle Applied to Art of War: "There are only five notes in the musical scale, but their variations are so many that they cannot all be heard. There are only five basic colors, but their variations are so many that they cannot all be seen. There are only five basic flavors, but their variations are so many that they cannot all be tasted. There are only two kinds of charge in battle, the unorthodox surprise attack and the orthodox direct attack, but variations of the unorthodox and the orthodox are endless. The unorthodox and the orthodox give rise to each other, like a beginningless circle -- who could exhaust them?" - Sun Tzu
The Enso Circle: "The enso is a circle that is hand-drawn in one or two uninhibited brushstrokes to express a moment when the mind is free to let the body create. The ensō symbolizes absolute enlightenment, strength, elegance, the universe, and mu (the void). It is characterised by a minimalism born of Japanese aesthetics. The circle may be open or closed. In the former case, the circle is incomplete, allowing for movement and development as well as the perfection of all things. Zen practitioners relate the idea to wabi-sabi, the beauty of imperfection."