Why Not Quit?

The new patient was airing his woes to an understanding doctor. "After the first, I\'m tired, Doc. After the second, my chest aches and I start getting pains in my legs. After the third, I feel like fainting and it takes half-an-hour for my heart and respiration to return to normal." "Why don\'t you quit after the first?" inquired the doctor. "How can I do that, Doc?" said the patient. "I live on the third."