Here the key pointers: Behrman was a man who was never respected. He always spend his life in part time jobs like being a model for other painters. But he always dreamt to paint a masterpiece. When he came to know about johnsy's condition he decided to save a her life. He painted a last leave in such a realistic manner that Johnsy n Sue didn't understand that how a leaf an be steady in this wind.
Behrman was able to paint the last leaf on the vine.Mrs. Johnsy ,struggling with pneumonia , made up her mind that she shall die the day the last leaf would fall.But the night the last leaf fell , Behrman , the skilled artist painted it there . Seeing the determination of the last (fake ) leaf , Johnsy decided that she should leave that thought of dying.Her confidence made her stand upright and free from disease.

Summary of this story by O.Henry is that we should have the determination , and then anything is not impossible.'
In this way , Behrman's masterpiece was able to save a life