योगश्चित्तवृत्तिनिरोधः Yogaś-Citta-Vṛatti-Nirodha:
The bottom of a lake we cannot see, because its surface is covered with ripples. It is only possible for us to catch a glimpse of the bottom, when the ripples have subsided, and the water is calm. If the water is muddy or is agitated all the time, the bottom will not be seen. If it is clear, and there are no waves, we shall see the bottom.