Given the track record of economists, the wonder is that anyone pays any attention to them anymore. Their predictions are usually stated as loosely as possible, and even then they usually turn out to be wrong.
Correct predictions are as random as human behavior itself — which isn’t surprising, considering that predicting human behavior (more precisely, particular results following from human behavior) is exactly what economists attempt to do. There is, however, one hugely important, completely definite, very practical lesson that we can learn from economics.