People who are seriously helped by the program will not return, but those who were not helped will come back. Over the long run the program will be full of peop

People who are seriously helped by the program will not return, but those who were not helped will come back. Over the long run the program will be full of people who cannot be helped and a small number who will do well. So seeing 2 out of 10 doing well does not shed light on the program's success.