WHEN I have fears that I may cease to be
Before my pen has glean'd my teeming brain,
Before high pil`d books, in charact'ry,
Hold like rich garners the full-ripen'd grain;
When I behold, upon the night's starr'd face,
Huge cloudy symbols of a high romance,
And feel that I may never live to trace
Their shadows, with the magic hand of chance;
And when I feel, fair creature of an hour!
That I shall never look upon thee more,
Never have relish in the faery power
Of unreflecting love;--then on the shore
   Of the wide world I stand alone, and think,
   Till Love and Fame to nothingness do sink.

John Keats

http://www.poemhunter.com/poem/when-i-have-fears-that-i-may-cease-to-be/