The ideal setup for a crash is a consensus that a crash is impossible–in other words, just like the present: sure, there are carefully measured murmurings about a “correction” but nobody with anything to lose in the way of public credibility is calling for an honest-to-goodness crash, a real crash, not a wimpy, limp-wristed dip that will immediately be bought.
What I’m calling for is a rip your face off, weeping bitter tears over the grave of the speculative wealth that you thought was forever crash. All those buying the dip because the Fed will never let the market go down will be crushed like scurrying and all those trying to rotate into the next hot sector or asset class will also be crushed like scurrying cockroaches because when the Everything Bubble pops, well, everything pops. There is no shelter in a risk-off cascade.
The crash is coming as a result of multiple mutually reinforcing dynamics, the first being that no “serious person” believes a crash is possible, much less imminent. In no particular order, here are a raft of other causally consequential triggers of a cascading market crash: