This Entrepreneur Who Sold Her Company for $1 Billion Wants You to Throw Out the Unwritten Rules That Hold You Back 'Never accept the things that don't make sense,' says the Pink Ceiling founder and CEO Cindy Whitehead.

In this series, Open Every Door, Entrepreneur staff writer Nina Zipkin shares her conversations with leaders about understanding what you have to offer, navigating the obstacles that will block your path, identifying opportunity and creating it for yourself and for others.

After selling two companies for more than $1.5 billion, pharmaceuticals entrepreneur Cindy Whitehead wants to pay it forward and help other female founders launch their companies and succeed.

As the co-founder and CEO of Sprout Pharmaceuticals, Whitehead shepherded a drug called Addyi -- known as "the female Viagra" -- through the rigorous FDA approval process. It became the first FDA-approved drug geared towards women who experience low sexual desire.

Of her experience with the FDA, Whitehead says she learned a valuable lesson: "I think there are two versions of rules in society. There are the regulatory rules and the unwritten rules. … [The unwritten rules] are only there because we say that they're there."

If the only reason for a rule is that it's the way things have always been, then by all means, break it.

In 2015, the company was acquired by Valeant, and Whitehead knew that she wanted to start a new chapter of her life. She had spent 22 years in the world of healthcare and pharmaceuticals, an industry where only four percent of the businesses are led by women.

In 2016, she launched the Pink Ceiling, an organization dedicated to investing and championing companies made by and for women. To date, the Pink Ceiling has invested in seven companies, including IntuiTap, a medical device company that aims to streamline the spinal tap procedure, and Lia Diagnostics, the maker of a sustainable pregnancy test.

The Pink Ceiling's incubator -- dubbed, appropriately, the Pinkubator -- launched in February and recently completed a three-month mentorship program with a group of 50 female entrepreneurs.

"I never had a mentor, not in a formal way. What I learned is to find mentors to my left and my right. Everybody has something to teach you," Whitehead told Entrepreneur about the philosophy behind the Pink Ceiling. "I know the fault lines. I [want to] help them get there faster than I got there."

Entrepreneur spoke with Whitehead for more insights on finding partners that will have your back, how to derive power from being underestimated and the importance of empathy.

Related: The Success of 'Wonder Woman' Speaks Volumes About Opportunity

Why did you want to start the Pink Ceiling and what do you hope to achieve with it?

After my exit out of Sprout I really had an opportunity to take stock of what I loved and what I wanted to be doing. I wanted to help foster other entrepreneurs, and help them have the kind of exits I had. For me, fighting the injustices is really important, and the injustice I'm fighting with the Pink Ceiling is not only women's limited access to capital, but also their limited access to mentors.

If I look down the road with Pink Ceiling, I hope we've given back through mentorship, but I also hope we've made a lot of women really rich. I know by all the data, women will pay it forward. They will invest in their communities, in their families, in other women, they will go on to mentor others.

Related: Merrill Lynch Exec Turned Entrepreneur Sallie Krawcheck on Money, Power and Knowing Your Worth

What was a challenge that you faced in your career and what did you learn from it?

[With Sprout Pharmaceuticals] one thing I learned is to never accept the narratives that hold up progress. The narrative around female sexuality was holding up progress. You've got to push through. I was fortunate that women were willing to share their stories with me. When I heard the stories of these women, I thought, goddamit, other people are going to hear these women's stories too.

People used to push me and say, "Cindy, nobody is going to lose their life from this." And I would say, "But they might lose their life as they know it." They have relationships that end in divorce, they develop self-esteem issues. That was a really important part.

You have to be unapologetic in your mission. Even if you choose the road less traveled.

Related: ThirdLove Founder Heidi Zak on How to Develop Authentic Connections

When was there a moment in your career when you had to advocate for yourself? How did you approach it?

It is scary, but I made a decision early on. It was very clear that I was going to be underestimated. I don't look like a pharmaceutical CEO. I wear pink on purpose. Underpinned in that is a little bit of irreverence, and little bit of the fact that I'm not going to apologize for liking pink. With underestimation, you have two choices: You can either rail against it and be almost paralyzed in frustration or you can use it as an invitation to surprise people with your competence, almost harness it.

I stand in front of a room that's a sea of blue and grey suits in my pink talking about sex, believe me, the opening was giggles. I learned really quickly. I would put up brain scan images of women with the condition. I would go silent and I would point to the scan. I could go toe to toe all day long with all of the data. That surprised people.

No one thought that I was going to get the FDA approval. I think that my surprise factor was empathy. Women knew that I was doing it for the right reasons. Not to make the next blockbuster drug, but to actually give them access and choice. They could take it or not take it, I just wanted to give them the choice.

Related: This Fitness CEO Says You Should Own Your Failure So You Can Learn From It

What was a mistake you made in your career? How did you move forward from it?

From an entrepreneurial standpoint, the biggest mistake I made was taking money from someone I didn't trust. It was early stage, it was the ability to scale. When you're cash-strapped and somebody is offering you a check, it's hard to actually remember that you're choosing too. It's really important because they are going to be in this with you for the long haul.

So I took money from somebody who could not have been more philosophically different from me in how you treat people, how you compensate people. I had a contract in which I couldn't get out of it for a year with this company. To the minute I could cut the contract, I cut the contract. I had to swallow really hard and find someone to buy them out, which was not easy. At the time, it almost took down the business.

I built both businesses [Slate Pharmaceuticals and Sprout Pharmaceuticals] with angel investors, which is very unusual in pharma. But a lot of that was I was only going to find the individuals who really got what I was trying to do. If you look at the path I took with the FDA, I needed people in there who were going to go the distance with me.

Related: The Forgotten Hollywood Icon Whose Genius Made Wi-Fi Possible

What do you tell yourself during tough moments to keep moving forward?

In the darkest moments -- I think of this particularly with Sprout because it was such an incredibly up and down rollercoaster ride -- I would literally go back to my computer and read the emails that women were sending me.

The emails that said thank you for fighting the fight, thank you for reminding me that I'm not alone, thank you for telling me it's not in my head. The fact that they had opened the doors of their bedroom to me and their most personal struggle said to me, you've got to get this right. Win or lose, you have to take it all the way. All of the things I choose to do have a deeper purpose for me. So remind yourself of that purpose during those dark moments and the give up moments.