Was this market fall foreseeable? And if so, why didn't the market fall beforehand?

How does today's stock market activity mean in terms of a theory such as the Efficient Market Hypothesis?

And going forward, what should be the takeaways? Is this the start of a steeper decline? A time to sell stocks and buy bonds?

Is this a time to put all of your money from cash to stocks? Or slowly invest more over time?