Our Unicorn List will involve tracking these fast-growing, highly valued startups. We reached out to the founders and CEOs and asked a few questions. What does having a billion-dollar valuation (or higher) mean to you and your company? How does it change the way you operate? Is it a sign of success, or added pressure? We also asked about challenges and roadblocks along the way. What was your lowest moment or biggest obstacle on the path to where your startup is now?

We even asked them, if they were willing, to tell us about the moment when they closed the round that resulted in their most recent valuation, and where they were, and how it felt.

Here are some of the most colorful responses.

And be sure to read the cover story of our new issue: The age of unicorns.

Naveen Tewari, CEO, InMobi

"We never get caught up in the actual numbers, but it's a great club to be a part of. We went through lows and highs and spent many sleepless nights. I used to go to bed every night during our early years thinking we were going to fold the very next day. I guess some of that paranoia has gone."

Kenneth Lin, CEO, Credit Karma

"A billion-dollar valuation can be a double-edged sword. On one hand, it’s great for recruiting, brand recognition, and employee morale. On the flip side, big valuations often lead to more scrutiny from outsiders and sometimes they hinder innovation. There are quite a few low points in the life a startup. We were almost shut down 38 days after launching. We ran out of money on multiple occasions. Our biggest challenge was proving we weren’t like the other guys."

Adi Tatarko, CEO, Houzz

"While it's nice, [the valuation] doesn’t change the way we operate day to day. It’s still a crazy roller coaster ride with a lot of hard work."

Jyoti Bansal, CEO, AppDynamics

"It’s not like winning the lottery. There’s not a phone call you get and suddenly you’re a billion-dollar company. It was a process that took several months. It’s like making the playoffs—we haven't won the championship yet, but a ‘W’ is in sight. The biggest mistake people can make in these situations is to celebrate and forget that there are still more big and important games ahead."

Brian O'Kelley, CEO, AppNexus

"It’s kind of like opening a healthy lead halfway through a marathon: it’s much better than being behind, but now everybody’s gunning for you."

Dan Wagner, CEO, Powa

"If you start believing your own hype, you get distracted. As far as I’m concerned, the business is worth nothing until we’ve proven the value that we set out to create. The investment is just a sign we’re on the right path."

Ash Ashutosh, CEO, Actifio

"The analogy we use is when you see a duck on water. It looks smooth and easy on top, but underneath it’s paddling like hell. You’ve got to work extra hard to make it look extra easy."

Tomer Bar-Zeev, IronSource

"Speaking generally, this valuation means we must be doing something right! But you don’t succeed in this industry by getting complacent and congratulating yourself, so my immediate concern was more on how we could build on the amazing growth than on the win itself."

Kunal Bahl, CEO, Snapdeal

"As we know, in the tech space, things yo-yo quite drastically, so you need to keep a balanced mind about valuations. However, there is always a feeling of disbelief that we created a company that is worth the kind of valuation that we only read about in Fortune. Just a few years ago we were working out of the 200-square-foot basement of a house in a run-down furniture market in New Delhi. Less than two years ago we were down to less than $100,000 in the bank."

Matt Mullenweg, CEO, Automattic

"It's great to have external validation of our progress, but ultimately all that matters is the happiness of our customers. Even though we're perceived as very successful, we face dozens of major setbacks every year, it's just a matter of working through them."

Kurt Graves, CEO, Intarcia

"As a private company, to have a valuation close to $2 billion, like we do, is recognition that we have something special on our hands. It's only scratching the surface of what I think the real value of the company is. So we’re not at all satisfied."

Tom Reilly, CEO, Cloudera

"In and of itself, the valuation means very little... Until the company is traded publicly or acquired, that value has not been achieved... The valuation does mean that we get a bit more attention from investors, media, industry analysts and prospective employees."

Kevin Chou, CEO, Kabam

"A $1 billion valuation catapults us into a new realm. The crash of 2008 resulted in our company losing 90 percent of its revenue.  Within a year, we transformed our business. We had no idea if we would succeed, much less reach a $1 billion valuation five years later."

Pieter van der Does, CEO, Adyen

"Our valuation means we are in a very select group. It means we can further increase the gap between ourselves and our competitors who are trying to catch up."

Dheeraj Pandey, CEO, Nutanix

"It's merely a milestone in the journey... a small validation. We've faced two near-death product experiences, in late 2011 and early 2013, and we had to 'change the wings of the plane while flying at 35,000 feet.' Such resilience defines us. As they say: fortune favors the brave."

Stewart Butterfield, CEO, Slack

"We drove the valuation, so it wasn’t a surprise, but now we have to get to work. It’s a good thing for the business for sure, but if you work here, I try to make sure everyone feels the pressure that comes with it. It’s a positive feedback loop. You get the high valuation, so it’s easier for us to higher smarter people, so it’s easier to deliver on the product side, so it’s easier for us to grow. It definitely helps."

Michelle Zatlyn, Co-founder, Cloudflare

"Our valuation is something we’ve never focused on internally. It’s just not a topic. It's a moment to step back and say, ‘Wow, this is what other people in the market perceive that you’ve built.’ Even when things go really well—and again I think we’ve been very fortunate—bad things happen all the time. [I want to] make sure that we reach our full potential. That weighs on my shoulders."