Eternity.

You must live in the present, launch yourself on every wave, find your eternity in each moment. Fools stand on their island of opportunities and look toward another land. There is no other land; there is no other life but this.  The intellect of most men is barren. They neither fertilize or are fertilized. It is the marriage of the soul with nature that makes the intellect fruitful, that gives birth to imagination…without nature-awakened imagination most persons do not really live in the world, they merely pass through it as they live dull lives of quiet desperation.

- Henry David Thoreau