"When we try to understand this issue, it helps to remember that if bad luck were the main cause of homelessness, good luck would suffice to end it. Luck is by definition always changing. Thus if bad luck were the main cause of homelessness, most people would be homeless occasionally, but few would be homeless for long. In reality, most people are never homeless, a sizeable number are homeless briefly, and a few are homeless for long periods. The long-term homeless are mostly people for whom almost everything imaginable has gone wrong for many years. Many are heavy drug or alcohol users. Many have severe mental disabilities. Even those who do not have such easily labeled problems have the kind of bad luck that recurs over and over, causing them to lose one job after another and one friend after another. In such cases it makes more sense to speak of bad karma than bad luck.
Sympathetic writers and advocates often dwell on bad luck because they want to convince the public that the homeless are victims of circumstances beyond their control and deserve our help. This strikes me as a myopic strategy. It inspires incredulity among the worldly, and it leads the credulous to underestimate how much the long-term homeless really need. If bad luck were the main cause of long-term homelessness, we could solve the problem by giving everyone on the street a shower, clean clothes, a job at McDonald's, and a roommate. Sometimes that is all the homeless need, and surely we should offer it. But many need a great deal more."
(from p47 in "The Homeless" by Christopher Jencks)