Silicon Valley's best and brightest tech companies will need to take it on the chin, and settle for lower valuations when they eventually go public.

So says Bill Gurley, general partner at Benchmark, one of Silicon Valley's most influential venture capital firms.

Gurley has been warning for months that the record valuations achieved by some of the Valley's hottest tech startups are unsustainable. Currently there are 142 startups with valuations of $1 billion or more, according to venture capital research firm CBInsights.

"Liquidity is the only real measure," Gurley said in a live interview at a technology conference hosted by the Wall Street Journal, in Lagunas, California. "All these private valuations are fake. They're all on paper."

Gurley's insights from the talk might read like a check-list of basics for all startups, but for today's founders they should feel even more relevant. Here are three big takeaways:

1. Count on tough questions.

If you're looking for investor cash, particularly if you're in tech, expect to be more closely scrutinized.

2. Give your investors an exit strategy.

Whether that's thorugh an IPO or an acquisition, even the most patient investors are counting on your business to generate returns. In today's enivronment of seemingly easy and plentiful investor cash, more companies have opted to stay private for years, rather than go public.

3. You can't just burn through cash.

At some point you have to prove that you can make some money. "We have gotten very comfortable with $20 million a month burn rates," Gurley said. "When did this become okay?"

Yet Benchmark has helped create some of these enormous valuations. In recent years, its investments have helped push ride share company Uber's worth to a stratospheric $50 billion. Similarly, it invested $21 million in an early round in messaging app Snapchat, which is now worth $16 billion. And office share company WeWork is now valued at $10 billion, thanks in part to the nearly $1 billion its raised with Benchmark's help.

"Every single one of these companies is going to get evaluated over time in a more scrutinous manner," Gurley reportedly said.