It begins with a highly complex financial system, whose very complexity makes it difficult for anyone to know what might be going wrong; by definition, the multiple parts of the financial system are linked, which means that trouble in one institution, city, or region can travel easily and quickly to others.

Buoyant growth in the economy makes the financials system more fragile, in part due to the demand for capital and in part due to the tendency of some institutions to take on more risk than is prudent.

Leaders in government and the financials sector implement policies that advertently or inadvertently increase the exposure to risk of crisis.

An economic shock hits the financials system. The mood of the market swings from optimism to pessimism, create a self-reinforcing downward spiral.