Hint Water CEO Kara Goldin's Most Important Factor for Success: Relentlessness The founder achieved her success by changing the beverage industry. Now she's trying to change Washington's approach to clean water.

When someone tells Kara Goldin why she can't do something, she replies in the same way: "What can we do?" After all, something has to be possible! That attitude helped her turn her life around, and it led her to create the popular beverage brand Hint Water. As she writes in her new book, Undaunted: Overcoming Doubts and Doubters, the journey began after she left her job at AOL in 2001 and tried to improve her health. She struggled to kick a diet soda addiction, couldn't find anything unsweetened in the marketplace that she liked, and set about building a lightly flavored, sugar-free water. Despite many manufacturing and retail challenges, she succeeded — and now, like in this conversation, she urges other entrepreneurs to approach their challenges "undaunted."

In your book, you write about a hard conversation you had with your husband in Hint Water's early days. You write, "We had no manufacturing partner. We were running out of inventory. We were burning through money. We had four kids at home, in a house in the most expensive city in the country. What the hell were we doing?" Many entrepreneurs ask themselves that question. What got you through it?

It's easier to get through that moment when you start to hear from customers. They were writing me from day one, saying, "I've lost weight since I've started drinking your product. I've controlled my type 2 diabetes." So whenever I faced a super challenging time, or decisions needed to be made about whether or not we were going to move forward, I thought, If we go away tomorrow, then there's these people out there that actually really love the product. I would literally go back to these emails or remember the phone calls I had with these people.