At the end of O. Henry's "The Last Leaf," there is his signature ironic reversal that suggests that Johnsy's fate has been controlled by more than her belief in the strength of Nature.
The little Jewish curmudgeon, Behrman, has argued with Sue that no one could be so silly as to die "because leafs dey drop off from a confounded vine?" He scoffs at Sue's having allowed Johnsy to think such ridiculous thoughts: "I haf not heard of such a thing....Vy do you allow dot silly pusiness to come in der brain of her?" However, unbeknown to Sue--and of course to Johnsy--the little artist has painted a leaf upon the wall across from Johnsy's window to ensure that she will believe in the strength of nature, and, therefore, desire to live.
"[L]ook out the window, dear, at the last ivy leaf on the wall. Didn't you wonder why it never fluttered or moved when the wind blew?"
And so, at the end of the narrative, Johnsy has been tricked by Behrman, but his artistic deception, his masterpiece for which he needed inspiration, has resulted in Johnsy's calling up her inner strength. Sadly, in an ironic reversal, Behrman has ironically sacrificed himself to save the girl as he, then, contracts pneumonia from having been out so long in the cold, rainy night and dies.