Inc. asked the nation's fastest growing, private-company CEOs to answer a series of wide-ranging questions about their early days and their biggest struggles. Here's how they launched and how they stay motivated, as well as what keeps them up at night.

Sixty-nine percent said leading a company was what motivated them to be an entrepreneur. What worries Inc. 500 CEOs about starting companies? Most cited failure (nearly 50 percent), followed by concern for their workers' livelihoods. That concern persists: Many said the hardest part of being a founder was maintaining others' jobs--even while providing jobs was often cited as one rewarding aspect of having a company.

Seventy-six percent of CEOs used their personal savings as startup capital. And if that's not bootstrappy and daring enough for you, the next most common source for founders' capital was credit cards. And most CEOs didn't look too far when it came to starting their companies: 35 percent of survey respondents said partners and co-founders had been work colleagues, followed by 33 percent who said they started up with a close friend.

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Q: What is the hardest thing about being a founder?

A: "My spouse had not been through this process before in any way and had no entrepreneurs in her family. This has been a foreign and very scary experience for her." -- Henry Jones, Kopis Mobile | No. 384

A: "I've spent the past 12 years of my life fight or flight. It is a strange way to live." -- Michael Baker, Mosaic451 | No. 376

A: "The hardest thing about being a founder is that you always have to come up with an answer, even if you are not sure if it is correct." -- John Saruwatari, Blossom Ridge Home Health & Hospice | No. 404

A: "Knowing that I'm responsible for the livelihood of my employees and for living up to my investors' expectations." -- Samer Hamadeh, Zeel | No. 167

A: "Creating two days and nights in 24 hours to get job done. Different time zones: manufacturing in China, IT in India, sales in USA/Europe." -- Neel Kulshreshtha, Skull Shaver | No. 347

A: "Managing my own emotions." -- Sarah LaFleur, MM.LaFleur | No. 43

Q: What is the best thing about being a founder?

A: "The ability to structure my schedule for meaningful time with my children." -- Eric CorL, Idea Buyer | No. 165

A: "Freedom, kind of." -- Calvin Tran, Hype Well Media | No. 195

A: "I might have to work 20 hours a day, but at least I get to decide when and where." -- Darold Rydl, PB&J Labs | No. 486

A: "Being able to provide opportunities to my employees that allow them to live the life they would like to." -- Kym Faylor, Azzur Labs | No. 132

A: "There's a daily fulfillment that I never experienced from a 9-to-5 job." -- Kyle Taylor, The Penny Hoarder | No. 25

A: "The way you become stronger with every challenge you overcome." -- Russell Ruffino, Clients on Demand | No. 186

A: "Being a job creator. There is a satisfaction in giving people a career." -- Alan Redmond, National Brokers of America | No. 154