This made me think about fishing and all the external forces that affect the catch. Is the tide coming in or out? Is it hot, cold, summer or winter? What time of day is it? Is the sun out? Is the river flowing gently, or angry and swollen? Sometimes these forces over which you have no control, mean you return empty handed, others, with a full bag. If you stop fishing, a zero catch is guaranteed.

All the forces cycle through the different states, like a wheel. Sometimes they synchronise into forward motion.