When that collapses, you're stuck with a sheepish grin and a lot of unhappy people.I think we will see Zestimates "correct" for the next 6 to 12 months while they sort things out and try to keep the SEC (and investors) out of their offices in Seattle. 

He has predicted just about every asset collapsing for 30 years.

Plus, Portland has gone to H-ll and it needs to collapse and rebuild or at least change the city mayor and city council before investing will do you any good there.

If an accepted offered has such conditions for the benefit of the buyer, they may well be able to either renegotiate the price, based on discovery, or collapse the deal.

War in Ukraine, War in Taiwan, War in North Korea, Covid-25, serious change in election results, China economy collapse, maybe a change or advancement in AI that wipes out IT middle/senior managers or some other industry like health care. 

Is it about to collapse into the street? 

All of the ancillary businesses that depend on constant buy & sell of housing start to collapse - furniture stores, refinance officers, real estate agents. 2.

The developer who built the property took out a $300K mortgage and then tried to sell it for $399K right before the market collapse. 

I'd rather be in debt like the US, but with a reasonable workforce to pay it off than better capitalized but with a looming demographic collapse like these other countries/regions. 

Nuclear War, Biological contamination, a Carrington event, an EMP attack, complete collapse of western society, 3 D printers that can build a house in 24 hours, the caldera at Yellowstone blowing, the zombie apocalypse, the rapture.