Sheryl Sandberg is painfully building muscles.

Emotional and professional ones, that is. The chief operating officer of Facebook and co-author of Option B, a recent memoir about her husband's sudden death, on Tuesday spoke extensively about her unexpected, unwanted training regime.

"I couldn't get through it, in the very early days," she told me at Inc.'s GrowCo Conference in New Orleans. "And what I learned is, we don't have a fixed amount of resilience. It's a muscle--we don't only build it in ourselves, we build it in each other."

That's the main point of Option B, which Sandberg wrote with longtime collaborator and Wharton professor Adam Grant. But that message about resilience and repetition also underlay many of Sandberg's other remarks at the conference, even those more focused on business advice and Facebook's efforts to get more small-business users.

"The more resilient a company is, the bigger its chances of success are," Sandberg said during an on-stage interview with Inc. editor in chief Eric Schurenberg. "And it's not success that makes us resilient, it is failure ... both the big failures and the small ones."

Sandberg underlined this point in a Facebook post after the conference, praising the resilience of some of the entrepreneurs she met at GrowCo.

Facebook has had plenty of failures over the course of Sandberg's nine years there, which only help prove her point about the power of resilience; last week, the social-media giant reported $8 billion in first-quarter revenue and nearly two billion users worldwide.

Sandberg, whose remarks at the conference largely focused on Facebook's mobile goals and products for small businesses, said that entrepreneurs could succeed by following some of the effective decision-making habits that she and founder-CEO Mark Zuckerberg have developed.

"We talk about ruthless prioritization--what we mean is, only do the best of the ideas," Sandberg told me. "Lots of times there are very good ideas, but they're not as good as the most important things."