The 2008 Financial Crisis
A towering pyramid of mortgage debt, built on the belief that house prices could only rise and sliced into securities almost no one understood, collapsed and nearly took the global banking system down with it. Governments spent trillions to prevent a second Great Depression. Almost no one in a position to stop it had believed house prices could fall nationwide at the same time.
Credit expands faster than the real capacity to repay; the gap is eventually closed by crisis, default, relief, or reset.