&gt; Funny - you could say the same about physics. For example, knowing that the coming car may kill a person causes the human behaviour to change, namely the driver will stop the car. Does that invalidate Newton&#x27;s laws?<p>The difference is that whether a person will try to move out of the way of an oncoming car is <i>not</i> considered within the domain of physics (so them using their knowledge of physics to predict that a car is a danger may change their behavior, but not the accuracy of what physics predicts within its domain), but whether or not a person will try to move their money out of the path of a predicted stock market collapse <i>is</i> within the domain of economics.<p>This doesn&#x27;t actually make empiricism any less applicable to economics, but it does compound problems in the empirical study of economics.