What is the importance of the North End of Boston in the book, The Death and Life of Great American Cities?

The North End area of Boston is used by Jacobs as an example of what's wrong with the theory in public planning. The North End area is a slum, but its businesses and housing owners plow their revenues back into the community to redevelop the area. Jacobs visits the area and finds a rehabilitated, redeveloped and thriving community, yet the area does not qualify for large amounts of bank loans because it is classified as a slum. Jacobs claims this area is evident of what is wrong with the theory of city planning.