A man may run on confidently for a time, thinking he has her under his thumb, and shall one day exhaust her, but he too must at last be silent, and men remark only how brave a beginning he made; for when he at length dives into her, so vast is the disproportion of the told to the untold, that the former will seem but the bubble on the surface where he disappeared.
 Henry David Thoreau, A Week on the Concord and Merrimack Rivers (1849). copy citation

Context

“It were vain for me to endeavor to interrupt the Silence. She cannot be done into English. For six thousand years men have translated her with what fidelity belonged to each, and still she is little better than a sealed book. A man may run on confidently for a time, thinking he has her under his thumb, and shall one day exhaust her, but he too must at last be silent, and men remark only how brave a beginning he made; for when he at length dives into her, so vast is the disproportion of the told to the untold, that the former will seem but the bubble on the surface where he disappeared. Nevertheless, we will go on, like those Chinese cliff swallows, feathering our nests with the froth, which may one day be bread of life to such as dwell by the sea-shore. We had made about fifty miles this day with sail and oar, and now, far in the evening, our boat was grating against the bulrushes of its native port, and its keel recognized the Concord mud, where some semblance of its outline was still preserved in the flattened flags which had scarce yet erected themselves since our departure;” source