Say there's a traffic intersection where you, as the mayor, have observed there's been an increase in deadly traffic accidents. You decide that a solution (traffic lights, speed cameras etc) would decrease the rate of accidents. You implement this solution and voila there are now less accidents. You conclude that the solution was the right one and you are very happy about it. So you come up with a policy to implement that solution to other similarly high accident intersections.

What's wrong with all of this?