From populist and badly-thought out policies, all sorts of undesirable consequences flow. The Coalition's cap on the number of skilled immigrants who can come to Britain in the 12 months following the general election is already causing damage.
Visa applications from researchers are being turned down. Businesses are finding it difficult to bring in highly-qualified staff from overseas. The Government has already had to make a special case of Premier League footballers from abroad.
And a report from the Home Affairs Select Committee suggests that we have not seen anything yet. The Committee estimates that the cap, when it is made permanent from next April, will affect only a fifth of immigrants at most since the rest of the flow is likely to come from the European Union (which by law cannot be restricted). This means that if the Government is to achieve its target of cutting annual net migration flows to the "tens of thousands" in five years it will have to tighten the cap still further.
The Committee also suggests other drastic measures will be needed to meet this target such as restrictions on the flows of international students, curbs on family reunions and an end to the right of immigrants to settle in the UK long-term. A more inhumane and economically inefficient system it would be difficult to imagine. Restrictions on foreign students, who earn British universities some £6bn a year in fees, would be especially bizarre at a time when the Coalition is telling UK higher education institutions to maximise their revenues.
The idea of an arbitrary cap on skilled migrants and a promise to bring migration flows down so significantly were policies designed to allow the Conservatives to pose as "tough" on immigration in the general election. But now they are in Government, tough has become foolish.
The signs are that the Government will try to fudge the problem by creating more loopholes. They would do better to drop the cap altogether and, instead, explain to the British public that a nation that wishes to experience a sustained economic recovery is in no position to shut its borders to talent.