Economists used to pretty much ignore the financial sector altogether. It was a black box that simply turned S (saving) into I (investment), and did so efficiently, and there was no need to get into the details.
Our modern financial system couldn't crash like those antiquated systems that were around during and before the Great Depression. There was no need to include it in our macro models, at least not in any detail, or even ask questions about what might happen if there was a financial crisis.
Economist's View, 2 February 2016
Economic theory discredited