Once more into my arid days like dew, 
Like wind from an oasis, or the sound 
Of cold sweet water bubbling underground, 
A treacherous messenger, the thought of you 
Comes to destroy me; once more I renew 
Firm faith in your abundance, whom I found 
Long since to be but just one other mound 
Of sand, whereon no green thing ever grew. 
And once again, and wiser in no wise, 
I chase your colored phantom on the air, 
And sob and curse and fall and weep and rise 
And stumble pitifully on to where, 
Miserable and lost, with stinging eyes, 
Once more I clasp,—and there is nothing there.
Edna St. Vincent Millay
http://www.poemhunter.com/poem/sonnets-05-once-more-into-my-arid-days-like-dew/