This article was posted here before (http://www.gladwell.com/2006/2006_02_13_a_murray.html) and suggests homelessness might be a power-law problem. Ordinary people who are homeless because of everyday misfortune don't stay homeless for long and don't contribute to the homeless problem--chronically homeless people, many of whom are either mentally ill or mentally adapted to life on the street, are the biggest part of the problem.
The power law in the article refers to the costs associated with individuals, and to the number of people that were found to have returned to 'normal' life.
So a relatively small number of people are responsible for the majority of the costs attributed to all homeless people (in that case mostly for hospital treatments), they stay homeless because they can't get out or don't want to get out.
Those homeless people that are very motivated to stop being homeless will usually do so, those that are mentally ill or serious substance abusers have little to no chance.
Those that have 'adapted to life on the streets', I find it hard to find fault with them, they chose that path, the problem is with 'us', the ones that are not homeless because we see them as a problem, but they might disagree.
Being homeless is no picknick, but being in the rat race isn't either and some people might prefer the one over the other.
