What men can learn from Sheryl Sandberg's Lean In

Facebook's Sheryl Sandberg and AmEx's Ken Chenault, laughing, talking, leanin'

Have you heard enough about Sheryl Sandberg? The Facebook COO-cum-author's career evangelism -- Go for that promotion! Break through those barriers! Dare to be CEO! -- can overwhelm (and, indeed, her book-related media blitz has). But largely missing from the buzz and debate over Lean In: Women, Work and the Will to Lead, is what her book, a No. 1 bestseller, means for men.

"Lean In is all about empowerment and accountability," says American Express (AXP, Fortune 500) CEO Ken Chenault, one of the Fortune 500 CEOs whom Sandberg has conscripted in her crusade to change the attitudes and behavior of managers across the corporate universe. "But the book is not just about women leaning in," Chenault says. "It's also about men leaning in. Success is a two-way street."

Chenault and Sandberg met five years ago, just after Sandberg arrived at Facebook (FB) from Google (GOOG, Fortune 500), where she was VP of global online sales and operations. Chenault, who was earlier to the digital revolution than his financial services brethren, visited Silicon Valley regularly -- he still does. They instantly hit it off. Sandberg even had Chenault speak at one of her "Women of Silicon Valley" gatherings at her Atherton, Calif., home.

He ranks high on her scale of evolved corporate guys because he's not like most. Sandberg says that the majority of men don't mentor women at work, and she cites evidence that 64% of male bosses are afraid to be alone in a room with a female employee. Chenault, one of the first African-American CEOs of a Fortune 500 company, pushes mentoring at AmEx. "You've got to develop relationships," he says. "You can't do things just in a formal context." "We have to let men relax," adds Sandberg. "Informal conversation -- that's how relationships are built."

One thing these two don't agree on: the outlook for male-female parity at the top of corporate America. "The odds are very challenging," says Chenault, 61. Sandberg, 43, is more optimistic: "We have to get there." Asked whether a college kid who dreams of being a Fortune 500 CEO might be better off today as a woman or as a black man, Chenault replies, "I think it's going to be harder either way."

--Face to Face examines successful business partnerships that offer lessons on collaboration and compromise.

This story is from the April 08, 2013 issue of Fortune.