Percy Bysshe Shelley - Mutability

We are as clouds that veil the midnight moon;
How restlessly they speed, and gleam, and quiver,
Streaking the darkness radiantly!--yet soon
Night closes round, and they are lost forever:

Or like forgotten lyres, whose dissonant strings
Give various response to each varying blast,
To whose frail frame no second motion brings
One mood or modulation like the last.

We rest.--A dream has power to poison sleep;
We rise.--One wandering thought pollutes the day;
We feel, conceive or reason, laugh or weep;
Embrace fond woe, or cast our cares away:

It is the same!--For, be it joy or sorrow,
The path of its departure still is free:
Man's yesterday may ne'er be like his morrow;
Nought may endure but Mutability.

Percy Bysshe Shelley

http://www.poemhunter.com/poem/mutability/