The tables turned Wednesday morning at Fortune’s Most Powerful Women summit when CNN anchor Poppy Harlow posed the very same question to Engelbert. Having worked with Fortune 500 clients for three decades now, the Deloitte veteran had a ready answer.

Of the 500 companies on the list 60 years ago, only 65 (or 13%) are part of the ranking today. Even in the past 20 years, the change has been dramatic: Less than half of the Fortune 500 companies that were on the list two decades ago made the cut in 2015—or 43%.

All this goes to show that 10 years from now, we won’t recognize many of the companies leading the business world. And for companies that want to remain relevant, Engelbert says there are five big things they need to keep in mind:

1. Customer: The companies that will survive will be those that keep a relentless focus on the customer, constantly thinking about their businesses from an end-user standpoint.
2. Evolution: Businesses will have to keep reinventing themselves: “It’s better to be the disruptor, not disrupted.”
3. Eco-system: Playing nicely with others is key—there’s no way companies can make it on their own. Instead of competition or cooperation, the new business environment is one of “co-opetition.”
4. Employees: Being a great place to work is crucial—younger generations want increased mobility to do things differently.
5. Women: To survive, businesses are going to need a lot more women leaders.

On that last point, Engelbert herself is a perfect example of how the most successful companies are evolving. When she took on the role of CEO at Deloitte LLP in March of this year, she became the first women to ever hold the top job at a Big Four firm.

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