"Work-life balance is a lie," said TIAA president and CEO Thasunda Brown Duckett at Fortune's Most Powerful Women's Summit on Tuesday.

When she tried achieving a more balanced lifestyle, Duckett said, "It never reconciled. ... That 'S' on the chest wasn't for 'Superwoman.' It was for 'Spent.'

So instead, Duckett, who oversees more than $1 trillion of assets under management at TIAA, tried to live her life more like a well-diversified portfolio.

Here's what she meant: Take account of all the roles you play that matter most (e.g., employee, spouse, parent, sister, daughter, friend, etc.) and then divvy up your time across each, she suggested.

She reminded her fellow high-powered colleagues in attendance that no one has more than 100% of themselves to give, so allocations will vary according to need at different times in your life.

"Just like the stock market, it will have its volatility. So you give yourself permission to recalibrate. ... As a mom, my children don't get 100%, they get maybe 30%," Duckett said. But, she added, when her kids need it, that percentage goes up.

And as with a diversified portfolio, don't expect to outperform in every one of your investments every day. The goal is to "outperform this thing called life" over time, she said.

"In any given minute, I may not be the best mom. But over time, I'm a really good mother. On any given day, I may not feel like I am operating at my best as a CEO. But over time, I think I'm a pretty good leader."

Duckett took the helm at TIAA this past spring. Currently, she is just one of two Black women running a Fortune 500 company and the fourth ever to do so. She also is ranked 10th on Fortune's 2021 Most Powerful Women list.

During her session at Tuesday's summit, she stressed that she and others with influential platforms need to keep pressing for better representation of women and minorities both on boards and in the C-suite.