Homelessness can be caused by a variety of problems. The main cause is unaffordable housing for the poor. Secondary causes include mental illness, physical illnesses, substance abuse, lack of incentives to work, poor work ethics, and, like most social issues Grassroots.org seeks to address, lack of decent education. The National Law Center for Homelessness and Poverty reports that over 3 million men, women, and children were homeless over the past year – about 30% of them chronically and the others temporarily. In many cases people are in and out of the homeless system, which includes shelters, hospitals, the streets, and prisons. It is these chronic users of the system that utilize up to 90% of the nations resources devoted to the problem.