Spirals occur in nature (like the DNA molecule) and artificially (like a spiral staircase). There is an efficiency to spirals: one comes back around to where one has been before, but at another level -- perhaps with added height or perspective. Repetition is not recursion, but amplification: a spiral can expand the circumference of its circling, like a spiral galaxy.
I'm drawn to the spiral as a powerful metaphor because it is a model for iteration, and I am an advocate of iteration for learning and for developing meaningful content or projects.
I also like the spiral as a metaphor because it is a way of combining linear concepts (such as progress) with circular concepts (such as wholeness or eternity). Whenever I hear those water metaphors for the digital age ("surfing" the web, or the "drinking from the fire hose" of information) -- I like to substitute the spiral metaphor. It goes somewhere by circling back. And circling back is exactly what we often need to do if we are ever to move forward.
