The main thing you have to understand about macroeconomic theory — both of the type used by academics and the type employed by private-sector forecasters — is that it doesn't really work. Events are constantly taking macro people by surprise, counterexamples to pet theories are a dime a dozen, and the rare theory that can be tested against available data is usually rejected outright. In macroeconomics, your choice of model is usually between "awful" and "very slightly less awful."
Most macroeconomic theories can be easily tested: all we have to do is take a look at Japan. Japan has a number of unusual traits that make it a very good proving ground for macro models, including a shrinking population, inefficient labor markets, an economy out of sync with the rest of the world and a government willing to engage in dramatic economic experiments. Once we start examining theories used to explain the U.S. economy, and apply them to Japan, we find that these theories usually fail.
For example, take the theory of loanable funds, which is taught in most undergraduate introductory economic classes. According to this model, when the government borrows a lot of money, it pushes up interest rates. That makes a certain logical sense, since interest rates are the price of borrowing, and an increase in demand for credit should push up the price. But even as Japanese government deficits and borrowing have exploded since 1990, interest rates have done nothing but fall. So much for that idea. More demand for loans has been met with falling prices, not rising ones.