In 1973, Barbara Corcoran was a 22-year-old diner waitress from New Jersey with about 20 jobs under her belt. She borrowed $1,000 to start a real-estate company, selling apartments in Manhattan. In the intervening years, Corcoran grew her tiny startup, The Corcoran Group, into a $5 billion real-estate empire, selling the business for $66 billion in 2001.

We know her now as one of the savvy, high-powered investors on the hit ABC series Shark Tank. But her tenure on the show almost didn't happen. She had her contract in hand and was ready to get on a plane to California to start filming when she was told that the production team had decided to hire someone else. Undeterred, she wrote to executive producer Mark Burnett to let him know that she didn't view his dismissal as a failure, but rather a prelude to greater success. And the rest is history.

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In the six years that Shark Tank has been on the air, she has invested in more than 30 companies. Last year, she launched Barbara Corcoran Venture Partners, which gives people the chance to invest in businesses alongside the real-estate mogul. Corcoran is also a bestselling author, a motivational speaker and the real-estate contributor for The Today Show.

We caught up with Corcoran to talk about the value of quick decision making, approaching opportunities and obstacles with the same confidence and turning rejection into fuel for motivation.

Related: How Being Dyslexic and 'Lousy in School' Made Shark Tank Star Barbara Corcoran a Better Entrepreneur

Q: Knowing what you know now, what would you have done differently when you were first starting out?
I started my first business at the ripe old age of 22 because the boyfriend I met at the diner [where I worked as a waitress] told me I'd be great in real-estate sales. I liked my job fine but was ready for a change, so I quit my waitress job that day and got a job renting apartments in the big city. Turned out I liked the job and the city way more than I liked New Jersey.

I felt that I had the lucky break of a lifetime when the same boyfriend offered to loan me $1,000 to start my own brokerage business. I took the $1,000 and he took 51 percent of the stock and together we built a small company 14 men strong. He announced he was marrying my secretary 7 years later and sent my confidence in a tailspin I didn't pull out of for a full year. She was younger and prettier than me.

Here's what I wish I knew then that I know now. Building a business is little more than a series of quick opportunities followed by a big a series of big obstacles. The opportunities arrive and leave so quickly that they're way too easy to miss. If I hadn't quit my job on a stranger's suggestion the moment I heard it, I would have probably thought about it and not done it. Every great decision I've made in business since was made exactly that way -- quickly without any thought. I've learned that thought gets in the way.

Related: Shark Tank's Barbara Corcoran: 4 Things Successful Entrepreneurs Do

Q: What do you think would have happened had you known this back then?
A: Obstacles move in and park themselves on your chest. They're there to kill your spirit and take your confidence, and you need to spot them coming through the door and shoot them [and] not let them hang out. I didn't know that back then and could have easily lost my business. When my boyfriend left me, I gave it way too much thought, and as I analyzed what went wrong, what I lacked, how the business would not survive and what people would think, I lost my confidence. There were solutions all around as there always are, but I couldn't see them. I've since learned that you need to treat obstacles just like opportunity -- quickly without much thought and move on.

Related: Shark Tank's Barbara Corcoran: There's No Such Thing as Work-Life Balance

Q: What's one of the most valuable lessons you've learned in your career?
A: Six years ago a producer asked if I might want to invest my own money in businesses on a new TV show they were trying called Shark Tank. I agreed immediately and got the spot after great effort. When the contract finally arrived, I signed it without reading it. I bought three new outfits, packed my bags and booked my flight for Hollywood. When the producer called to announce they had hired someone else and they were sorry, I was devastated. But I had long ago learned how to move past obstacles fast instead of feeling sorry for myself and emailed the producer. I said that all the best things happened to me on the heels of rejection and I considered his rejection a lucky charm. I cited half dozen similar situations throughout my career where obstacles turned into my greatest opportunities and asked to come and compete for the job. Since then, I've enjoyed six great years on one of the most successful shows on TV.

Related: What This 'Shark Tank' Star Tells Herself When She Needs a Jolt of Confidence

Interview was edited for clarity and brevity.