The life of a wise man is most of all extemporaneous, for he lives out of an eternity which includes all time.
 Henry David Thoreau, A Week on the Concord and Merrimack Rivers (1849). copy citation

Context

“is then the motto of a wise man. For first, as the subtle discernment of the language would have taught us, with all his negligence he is still secure; but the sluggard, notwithstanding his heedlessness, is insecure. The life of a wise man is most of all extemporaneous, for he lives out of an eternity which includes all time. The cunning mind travels further back than Zoroaster each instant, and comes quite down to the present with its revelation. The utmost thrift and industry of thinking give no man any stock in life; his credit with the inner world is no better, his capital no larger.” source