Every bubble has money coming in from somewhere. There’s usually some kind of market distortion that leads to unnaturally dumb money. For example, a lowering of interest rates means that economic activity that was previously not profitable becomes profitable. It also means that risk tolerance increases as there is surplus from profitable areas of investment to make bigger bets. The main areas that the money has come in from for the current bubble since 2009 are quantitative easing and ZIRP and NIRP. Quantitative easing ended in 2014, but consisted largely of buying up various government backed securities from banks at prices that they probably wouldn’t get in the market. This money was then moved into mutual funds and so forth and drove the stock market bubble, which drove acquisitions which drove startup exits which drove bay area home prices, employee salaries and the cost of toast in San Francisco. All of this money has now been fairly widely distributed outside of the banking system, which leads to inflation, which leads to credit contraction due to central bank policy.
Where will the deleverage come from? Federal funds rates have been going up, and it takes about 2 to 3 years for the market to turn from when they first start going up usually which was the beginning of 2016. So the danger zone should start at about the beginning of 2018. Usually what happens first is volume dries up and then the rallies get weaker and weaker and one of the major indexes starts to diverge from the rest.
I think Bitcoin might weather the storm better than some assets as Bitcoins are harder to seize than cash, thus people might look to it as a safe haven against creditors.