Success stories are fun, but regrets? Those are even more interesting. The investors from "Shark Tank" recently sat down to rewatch some of their most emotionally fulfilling deals, and the reactions ranged from pride to outright kicking themselves for not going bigger.

The reaction video appeared on the show's official YouTube channel, with the Sharks and one featured founder sharing what was really running through their minds during those pressure-packed pitches.

Barbara Corcoran's Billion-Dollar Regret

When Cousins Maine Lobster rolled into the Tank, Barbara Corcoran put $55,000 on the table for 15% of the franchise food truck business specializing in lobster rolls. Looking back now, she had one thought: "I should've bought half of it."

Here's the thing: Corcoran was the only investor who didn't bail during the pitch. The other Sharks got spooked after digging into the company's finances and walked away. But that worked out beautifully for founders Sabin Lomac and Jim Tselikis, because Corcoran was exactly who they wanted.

"We had targeted Barbara going into this," Lomac revealed in the video. They were so set on landing her that they actually asked producers to reschedule their appearance to make sure she'd be there. "We really, really wanted Barbara."

The feeling was mutual from the start. "The minute I laid eyes on those guys I couldn't wait to hear what they had to say," Corcoran said.

Fast forward to today: Cousins Maine Lobster operates 85 trucks across more than 30 states and has generated over $1 billion in revenue since launching in 2012, according to the company's announcement earlier this year.

Kevin O'Leary Was Dead Wrong About Greeting Cards

Mr. Wonderful had his doubts about Lovepop, a company making 3D greeting cards. His initial thinking? "We're in the middle of a digital revolution. Who needs a card? That's what I was wrong about."

O'Leary invested $300,000 for 15% of the company anyway, and it turned into what he calls one of his best deals ever. "It's worth 10x that now, maybe 20," he said.

He wasn't alone in wanting a piece of Lovepop. Fellow investor Robert Herjavec offered the exact same terms, but the founders picked O'Leary. His response? "Eat that, Robert."

According to RocketReach, Lovepop now pulls in $168.9 million in annual revenue. Not bad for paper cards in the digital age.

Daymond John Chose Mentorship Over Money

One of Daymond John's most treasured Shark Tank moments doesn't involve writing a check at all. When 11-year-old Moziah "Mo" Bridges pitched his bow tie company Mo's Bows, John did something unusual: he convinced Mo to turn down everyone's money, including his own.

Instead, John offered something different. "I think the mentoring is way more valuable than the money," he said during the episode.

The decision was personal for John. Bridges had built his bow tie business with his mother and grandmother, which hit close to home. "That's exactly my story," John said in the reaction video. "That's me when I was 12 years old."

Mo's Bows has since generated more than $700,000 in sales and landed partnerships with the NBA, Cole Haan, Bloomingdale's, the Home Shopping Network, and Neiman Marcus, according to the company's website.

Sometimes the best investments aren't measured in equity percentages. Though if you're Barbara Corcoran, maybe next time go ahead and buy half.