The law of unintended consequences, often cited but rarely defined, is that actions of people—and especially of government—always have effects that are unanticipated or unintended. Economists and other social scientists have heeded its power for centuries; for just as long, politicians and popular opinion have largely ignored it. …
Most often, however, the law of unintended consequences illuminates the perverse unanticipated effects of legislation and regulation. In 1692 the English philosopher John Locke, a forerunner of modern
economists, urged the defeat of a parliamentary bill designed to cut the maximum permissible rate of interest from 6 percent to 4 percent. Locke argued that instead of benefiting borrowers, as intended, it would hurt them. People would find ways to circumvent the law, with the costs of circumvention borne by borrowers. To the extent the law was obeyed, Locke concluded, the chief results would be less available credit and a redistribution of income away from “widows, orphans and all those who have their estates in money.” (Concise Encyclopedia of Economics)
It's the poor who pay the price for ill-advised government "help"
A "must read" on this subject is The Economist's View of the World by Steven Rhoads (Cambridge, 1985). This University of Virginia professor explains what basic economic concepts people people need to understand in order to be effective public servants in the modern world. He then brings political wisdom to economics, explaining how a fuller, political perspective needs to supplement the economist's understanding of human affairs.