Henry Wadsworth Longfellow

Labor with what zeal we will,
  Something still remains undone,
Something uncompleted still
  Waits the rising of the sun.

By the bedside, on the stair,
  At the threshold, near the gates,
With its menace or its prayer,
  Like a mendicant it waits;

Waits, and will not go away;
  Waits, and will not be gainsaid;
By the cares of yesterday
  Each to-day is heavier made;

Till at length the burden seems
  Greater than our strength can bear,
Heavy as the weight of dreams,
  Pressing on us everywhere.

And we stand from day to day,
  Like the dwarfs of times gone by,
Who, as Northern legends say,
  On their shoulders held the sky.