I might have been leaning in, but I was bowing out of my power to choose and own the worth of my work.

A wise woman once told me that we write the book we need to read. Was that ever true for me! Writing No Excuses: 9 Ways Women Can Change How We Think About Power forced me to confront my pattern of giving away power, and that shook me to my core.

I am a former president of Planned Parenthood Federation of America and have been a leader in the women's movement for 30 years. But despite a career many people deemed amazing, my awareness of my own struggles with power began creeping up on me like a blush in 2008 when I wrote an article for ELLE magazine about the lack of women in political office.

I studied many organizations that train women to run for office and fund their campaigns. To my dismay, these organizations are scarcely moving the dial. At the rate we’re going, it will take another 70 years for women to reach parity in elected office. (Yes, even after much-touted 2012 gains to 20% of the Senate, we’re still on course for that 70-year trajectory.)

Shocked, I set forth to discover why. When women run, they’re just as likely to win as their male counterparts. But according to American University professor Jennifer Lawless, women are half as likely as men to think seriously about running and one-and-a-half times more likely than men to say they would never run.

You can’t win if you don’t run. If women don’t run, we’ll always be reacting to laws made by people who might not have our best interests at heart, or simply don’t understand the impact of policy through a gender lens.

Then I found the exact same dynamics, with exactly the same consequences, in the workplace and in intimate relationships.

Drilling down further, it became clear that the reasons are rooted in most women’s ambivalent relationship with power. I realized we must deal with our culturally-learned resistance to embracing power if we ever want to dismantle the remaining structural barriers to women's advancement.

But it was easier to digest the hard truth about women in general than to face my personal power demons. Then, while I was researching "No Excuses," another book I wrote with actress Kathleen Turner neared release. At our pre-release publicity meeting, though I was an equal partner contractually, the publicity director turned his back to me and spoke only to Kathleen.

In that moment, I realized I had done it again—I had spoken in someone else’s voice, not my own. And I had been doing it my whole life, despite rising from teen mom and high school dropout to president of Planned Parenthood. I became a best selling author (my dream since I was five years old!) and even taught a college course called “Women, Power, and Leadership,” but I still described my accomplishments as though they were happenstance: “I was lucky," "other people pushed me to do big things," "I simply responded to what was needed.”

I might have been leaning in, but I was bowing out of my power to choose and own the worth of my work. That was the moment I knew I had the power to shift from reaction to intention. I felt a tremendous relief.

The unwillingness to embrace power and the responsibility—and credit—that comes with it turns out to be a key difference between how women and men approach their work and their lives.

We don’t need to become men to change this pattern. We do need to value ourselves more, and to transform the power paradigm from a constricted “power over” to the expansive and positive (and more authentically female) “power TO” make life better for ourselves, our families, our companies, the world.

I’ve been an activist for women for 40 years, and as much as I'd like to, I can't live another 70 years. So I decided to “Lean In” one more time to move women along faster toward our fair and equal share of leadership positions by the year 2025.

With co-founder Amy Litzenberger, I’ve started Take The Lead to provide information, inspiration and practical tools for women at critical stages of their lives and careers. We proudly join with LeanIn.org in this effort.

I’m certain in the deepest parts of my heart that unlimited possibilities beckon to create a world that will be more equitable and healthier for both men and women. There are no excuses this time. It’s up to us to Lean In and Take The Lead together.