Just to elaborate a bit more on the credit cycle concept. The current long-wave credit cycle begin after WWII, with the creation of the Bretton Woods monetary regime, the IMF and World Bank, and the emergence of King Dollar as the undisputed global reserve currency. As this chart of the S&P illustrates, it's been a great run over the past 65-ish years. You'll also notice that the end days of the current K-wave cycle is clearly marked in 2000. After 2000, you'll also see clearly that there have been 2 major business cycle credit cycles since 2000: after bottoming in October 2002, there was a credit cycle from late 2002 to 2007/2008, and then another beginning in 2009, and that is currently within a year-ish away of ending IMO.
The current K-wave cycle emerged as a result of the collapse of the previous K-wave cycle, whose transition started with the onset of WW1, and whose final death was not witnessed until the end of WWII. This K-wave collapse saw the end of the Britian empire, and equally important, the collapse of the gold standard (first in WW1, and then the collapse of the so-called Gold Exchange standard in the late 1920s/early 1930's). The end of the US Dollar regime will likewise be supplanted by a new monetary regime, likely based around a combination of the Chinese Remnimbi, the German Deutschemark, and the US Dollar (and perhaps a return to gold as a monetary unit).
Anyway, I think one has to be very cautious extrapolating the upward trajectory of financial assets over the past 4 years to the next 2 years. We are late stages in the current business cycle credit cycle, and the next downturn will likely be vicious IMO.
That's the theory anyway.