You Might Not Want to Hear This Tough-Love Advice From Barbara Corcoran — But She Says It's the No. 1 Key to Success The founder and investor joined several other "Shark Tank" judges for an Advertising Week panel discussion.

There's no shortage of resources for aspiring entrepreneurs who want to learn what it really takes to start and grow a successful business. But perhaps some of the best authorities on the subject? Shark Tank's deal-savvy judges.

Earlier this week, Barbara Corcoran, Mark Cuban, Daymond John, Kevin O'Leary, and Lori Greiner came together for an Advertising Week panel in New York to celebrate 15 seasons of ABC's Shark Tank and share the business insights they've gleaned over the course of the show.

Related: Barbara Corcoran on the 5 Traits All Successful Entrepreneurs Share

During the discussion, which was moderated by the CEO of Thrive Global, Arianna Huffington, an ever-relevant question arose: What do small business owners need to know in order to succeed?

Several suggestions were batted around from the start: embracing and learning about AI, having a healthy dose of "fiery" ambition, staying curious, knowing how to reach customers and measure the cost of advertising, and, as always, brainstorming a great idea that solves a problem for a lot of people.

Corcoran sees the value in all of the above. But the real-estate brokerage founder and investor says it's just "trimmings" and "not the core of what makes an entrepreneur." And she's especially wary of chalking up success to having a "great idea."

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"I've invested in a lot of businesses with great ideas," Corcoran explains, "and I don't find that they're [always successful]. In fact, that's often not the case."

Related: Barbara Corcoran Says Ask This One Question in an Interview

So what is the No. 1 key to success, according to Corcoran?

"I find that the businesses that do well [are run by] the people who have the stamina to get back up after they've had hardship," she says. "In fact, when I look at my really successful entrepreneurs and compare them to everybody else, the real difference I see is that they spend less time feeling sorry for themselves. It's as simple as that. They get a rejection, and they get up like a jack-in-the-box and say, 'Hit me again.' And if you have that kind of stamina in your gut, you become a great entrepreneur."