When potential has not been fully experienced, we feel that we already understand it. When we actually do experience potential, we feel that some aspect of our understanding must surely be lacking.
For example, when sailing out beyond the mountains and into the ocean, when we look around in the four directions, the ocean appears to be round; it does not appear to have any other shape at all. Nevertheless, the great ocean is not round nor is it square. The actual qualities of the ocean are inexhaustible: to fish it is like a palace and to an island it is like a necklace. But as far as our eyes can see, it just appears to be round.
As it is for the ocean, so it is for potential. Whether caught up in the dusty world or beyond our worldly frame of reference, potential encompasses innumerable situations, but we understand only as far as our eyes can see. We should remember that beyond being square or round, the full aspects of oceans and mountains are numerous and endless, and there are whole worlds in the four directions. Not only is the vastness of space like this: remember, this present moment and a single drop of water are also like this. (liberally adapted from Genjo Koan in Dogen's Shobogenzo)