What plagues the Indian banking system? To understand that, we may have to go back a few decades — to the former Federal Reserve chairman Alan Greenspan taking a leisurely bath in a tub. It is then that he thought of the term “irrational exuberance”, when he was writing a speech. It has since come to describe a dangerous optimism that can wreck the financial system, and a wave of that hit the Indian banking system from 2003.