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Etsy, Groupon, Paperless Post, Warby Parker, Wordpress are all huge companies that came from simple ideas. We’ve interviewed these founders and more and put together some of their best advice for entrepreneurs starting out.

Robert Kalin is the founder of the handmade-focused, e-commerce site Etsy – which since launching in 2008 has amassed over 22 million members and whose merchants sold $895 million in gross merchandize in 2012. Kalin says he got a piece of advice he never forgot.

“There is one piece of advice that I replay in my mind over and over and it’s if you’re going down the wrong path and you feel like it’s the wrong path, just turn around and get out of it, and a lot of times there are hard decisions to make.”

Groupon founder Andrew Mason has been in the news recently after being ousted from the company  he started. But while he is no longer at the helm, he did build a business that Google once offered to buy for $6 billion. His advice is to the point.

“Don’t listen to advice. Just figure out what you need to do on your own. You can read all the business books in the world, and there’s a lot of good stuff in there, but ultimately, go with your gut and do what seems right, don’t listen to what guy in some book is saying.”

Alexa Hirshfeld, one of the founders of Paperless Post, the online invitation stationary startup that has delivered more than 60 million virtual cards, believes testing your concept with real users before looking for investment money is extremely helpful in raising capital.

“When you have 2,000 users, you notice their preferences, their willingness to pay, their desire for more and it allows you to go and raise capital in a way that you can really be confident because you know there is someone on the other side that needs what you’re making.”

The guys behind Warby Parker have helped to disrupt the $65 billion eyewear industry. But co-founder Dave Gilboa said if they had listened to others, they would have never started.

“I think most people are risk- adverse. If you have an idea that you’re really passionate about and you want to start a business, most people tend to ask a bunch of other people for advice – and I think it’s the natural inclination of most people to look for why something won’t work, and I think people get discouraged because they ask 10 people. And most people told us if it was possible to sell glasses online, someone would already be doing it, but we really believed in each other and really believed in the idea that we had and decided to ignore all the skeptics.”

Siggi Hillimarson of Siggi’s skyr-strained yogurt started his company out of his apartment and now sells over 100,000 cups of yogurt a week. He says one key to success is to expect success.

“It’s important to plan for success. I never dreamed how fast this would pick up or how successful we have been, so maybe I didn’t plan enough to be as successful as we have been fortunate enough to have been. Plan for your dreams to get realized.”

“It’s great to work on something that you would do even if you weren’t being paid.”

That’s Matt Mullenweg who was one of the founders of Wordpress, the open source blogging platform that powers over 60 million websites, including Fox News and Fox Business.

“Like the thing that you can’t not do. You go to bed thinking about it and you wake up every morning thinking about it. [ You do this] for a lot of reasons: one you do a better job but two, even if it doesn’t work out, at least you did what you wanted, at least you followed your passion.”

Shamus Jones did what he wanted.  He quit his job and negotiated a free commercial kitchen to work out of from 10 p.m. to 8 a.m. He says hard work, which included pulling those all-nighters, was crucial to making Brooklyn Brine a million-dollar pickle company.

“I had a moment when I was waiting for all the jars to cool and I had to send my whole crew home – and it was kind of a beautiful moment because I was sitting here in this space (at the brinery). Nobody was here, very zen and just being able to reflect on: “Man, you got what you asked for, you are doing what you want to do – and it made it all worth it, you know what I mean?’”

This is a compilation from past interviews for the Fox Business series Young Guns. Christina is on Twitter @ChristinaScotti

Christina is on Twitter @ChristinaScotti