I read this in class today, it is a short excerpt from Orit Sen Gupta's book, The Heart of Practice.
"In practice, we develop our seeing, and with time we see more, and more subtly. According to the Yoga Sutra, and the Upanishads, this subtler seeing leads us to see things we never imagined we would see. For instance, when we are very attentive, we can actually see the diaphragm. It's a seeing even if it's not the seeing of the eye, and it is extremely precise.
Seeing can become endlessly subtle. We don't need necessarily to want it, or to ask for it, but we should know that once we've started on a path that it may lead us to places we didn't expect, didn't know about, and couldn't have imagined. Just as a child of five can't imagine his body and his thought when he will be fifteen, so we can't know where this path will take us and how we will perceive things as our vision develops. But we can say that if we persistently practice, our ability to see will deepen and widen."