https://www.youtube.com/watch?v=RJWW0LOzOlk&t=397s
By that definition (and what appears to be the consensus on this thread), what we have here is not a crash.
It isn't even a "bear market" yet either (in the most widely used definition of the term), according to S&P 500 closing prices thus far. VTI/VTSAX haven't closed at 20% down either.
You can use other definitions if you like, but it's easier to communicate when people don't make up their own.
To answer the OP's question, what I've learned in this, let's call it "correction", is that the kinds of things that happened before in the financial markets are probably the same kinds of things that will happen again. The reason we're told about certain kinds of risks is because they actually do happen. Assuming they won't is a bad idea. It's like good weather and bad weather, anyone who's been around for a while expects that we'll get both.
It also reinforces my opinion that many would do well to put their long-term investment money in a target-date index fund and stay the course.