Earlier quoted context omitted.
Not sure how much it will impact startups with saner valuations, but yes I do suspect we might see a unicorn apocalypse at some point in the future. If it happens it will unroll more slowly than a public market crash since these markets are mostly illiquid and private. What you'll see is former unicorns raising down rounds and a general regression of other valuations in proportion to how over-inflated they might be.…
You are not clueless. It's just nearly impossible to draw an actionable line in the sand where on one side your valuation is sane and on the other it isn't. You certainly can't do that in any kind of general sense. Every startup is by definition unique. And there's almost always a way to justify a higher or lower valuation for any given company.
If every living multicellular organism on Earth would have to create an account on your service for it to be worth X, X is probably insane. If you have no meaningful revenue, then in most cases a valuation more than one standard deviation among the mean for your sector and maturity is probably nutty.