The financial crisis began in 2007, which lead to historically low interest rates, which meant that borrowers of all sorts, especially of the highest corporate and the highest personal credit ratings, were able to and have been able to borrow billions upon billions of dollars at interest rates so low, that the nature and the reasons why money was being loaned out fundamentally was transformed. In other words, the interest rate of that money, whether that be of corporations or of individuals, became so low that business decisions were based upon this, essentially meaning that all those that wanted to leverage up their assets or add to their debt, were able to do so at historically cheap rates, perhaps never to be repeated, ever again. In addition, those that weren't so credit worthy, have been able to get loans at interest rates that are far lower than where they would normally be at, along with even having the opportunity and the access to that borrowed money, simply because the gap between what it costs the lender to loan the money in comparison to the recipient that borrows the money is wide enough, that a good profit will be made, even when taken into account, the normal default rates.
The primary reason why interest rates were driven down so low for such an extended period of time, was to help promote and to initiate economic growth by providing to corporations a very cheap supply of money which would allow the borrowers of that money to expand their businesses, their infrastructure, and their hiring of additional personnel; in addition to, aiding and abetting debtors of all sorts, to re-finance, re-service, or to borrow money at very low interest rates, so that they would remain solvent and not thereby default, which if this had not been done, could have turned a recession into a depression.
However, ten years later, the upshot of all this low interest rate borrowing costs, isn't the big expansion of growth that pundits would have expected, but in actuality, in a very large sense, the gaming by corporations and individuals of utilizing cheap debt to augment their positions, while penalizing those that are savers, with interest rates so low, that they are unable to earn any significant interest from their short term investments, such as money market funds, CDs, treasury notes, and their equivalencies. So that, savers, have suffered at the hands of those that are best able to manipulate and manage debt, in which those debtors, more times than not, on a corporate level, have utilized cheap money, not to invest back into their infrastructure and employment, but rather to provide richer dividends to their stockholders, to buy back common shares so as to increase their earnings per share, to refinance their debt to a lower rate, and to utilize cheap money for mergers and acquisitions or vertical integration.
The fundamental problems though with ultra low interest rates that have existed now for over a decade, is that if the less than pristine debtors cannot or barely can pay their debts, today, what then happens when these interest rates are normalized? Further, if a significant part of earnings growth for corporations has been because of their ability to leverage up ultra cheap debt in order to juice up, in one form or another, their earnings per share, what happens when that debt is no longer cheap? The probably answer to these questions, is a stock market crash and a very bad recession