With any new role, it can be easy to feel out of your depth.

Studies suggest that as many as 70 percent of people have suffered from a sense of inadequacy, or "imposter syndrome," at some stage in their lives. And it turns out, that's no different if you're the first lady of the United States.

Michelle Obama, in her new book "Becoming," reveals that she felt "overwhelmed," "unworthy" and "uncertain of [her] purpose" when her husband's appointment as president propelled her to become the country's first African-American first lady.

In fact, Obama said it wasn't until two months in, when she met with a group of schoolgirls from north London, that she figured out the real purpose of her role.

"At this point, I'd been first lady for just over two months," Obama writes in her memoir, released on Tuesday. "In different moments, I'd felt overwhelmed by the pace, unworthy of the glamour, anxious about our children, and uncertain of my purpose."

It was early 2009, and the Obamas were in the U.K. on their first official overseas visit. While President Barack Obama was meeting with officials, the then-first lady was invited to a government-funded, all-girls secondary school in London's Islington neighborhood. Like herself, the majority of the girls there were ethnic minorities from modest backgrounds.