Model failure is usually more interesting than model success.The success of a model doesn't confirm the theory on which it is based, since many explanations for an outcome are possible. The failure of a model shows that at least one of the assumptions is incorrect, including the usual assumption in economics that all things remain equal.
Thoughts on the use of Models in Economics
Arnold Kling | Mercatus Center–affiliated senior scholar at George Mason University and a member of the Financial Markets Working Group
ht Mark Thoma at Economist's View