The Gronkowski brothers share the No. 1 piece of advice that helps them succeed in sports and business

Brothers Rob Gronkowski, Gordie Gronkowski, Dan Gronkowski and Chris Gronkowski at The 2015 ESPYS at Microsoft Theater on July 15, 2015 in Los Angeles, California. 
Kevin Mazur | WireImage | Getty Images

The Gronkowski family is known for athletics: four brothers, Rob, Chris, Glenn and Dan, played in the NFL, while the fifth and eldest brother, Gordie, played Major League Baseball. Rob, 29, famously nicknamed "The Gronk," is set to be the highest paid tight end in the NFL, playing for the New England Patriots.

The siblings are also making a name for themselves as entrepreneurs.

"Being an athlete and always having to to push yourself to be better than the person next to you, it's the same thing in business," Dan tells CNBC Make It.

The Gronkowski brothers' portfolio includes Gronk Fitness, a training equipment business; Gronk Nation, an apparel brand; a podcast; and even a party bus for rent, Gronk Bus.

Chris Gronkowski, 31, who most recently played for the Denver Broncos, struck out on his own with his stainless steel protein shaker business, Ice Shaker. He appeared on ABC's "Shark Tank" in October 2017 and landed a $150,000 joint investment from Mark Cuban and Alex Rodriguez.

Since then, business has boomed: "We had $80,000 in sales when we pitched on 'Shark Tank,' and we've hit over $3 million in sales since then," Chris Gronkowski tells CNBC Make It.

Billionaire technology investor Cuban is happy with the deal too: "[I] love him," Cuban tells CNBC Make It of Chris. "He knows how to sell. He knows how to always be iterating and improving his processes and product."

ABC | Michael Desmond | Getty Images

Dan, who runs Gronk Fitness along with Gordie and is responsible for e-commerce operations, also has his own project called Herd Chew, an all natural replacement for chewing tobacco made with Valerian Root and White Willow Bark.

"We just keep coming up with stuff," Dan Gronkowski, 33, tells CNBC Make It with a laugh.

So where do the siblings get their hustle from? Dan and Chris say they picked up their business acumen from their dad, Gordon Gronkowski, who was an entrepreneur himself.

"He started a business in 1990 called G&G Fitness Equipment out of Buffalo, [New York]," Dan says. "That was when we were a young family, and [he] put all of his money in, was working two jobs for probably eight or 10 years to get the business going.

"We were always around the stores," Dan says.

The company now has over 80 employees and store locations along the east coast.

When they were growing up, Gordon Gronkowski encouraged his sons to be competitive in sports, training them with fitness equipment in the family basement. And, he was careful to teach them that success isn't won without determination.

"The boys never got anything unless they earned it," Gordon Gronkowski told Kiplinger in 2016. "They all had a paper route. They saved money for hockey equipment, baseball bats; they had to buy that stuff. If you want something, you have to work hard for it."

Today, Chris says his father is still reminding him of that lesson. When he was first launching Ice Shaker, Chris excitedly ordered a preliminary shipment of 10,000 units, expecting the business would take off immediately.

"It was a brand new company, we were building it from the ground up, I had all this confidence that it was the best thing in the world," Chris remembers. But soon, his dad stepped in with some perspective.

"He was the one who talked me down, and said, 'Hey, you don't have any customer loyalty, you don't have a brand yet, you have no reviews — no matter how great you think your product is, no one else knows about it," Chris says. "It's not just going to happen over night. For me that was definitely the biggest and best advice I got.

"Nothing's easy. Nothing is going to come easy," he adds.

For Dan, their father's advice is about consistent effort over time.

"He's really about being patient," Dan adds. "Very few people [do] something that hits instantly and they're millionaires and they don't have to work again. It's all about building your brand, being patient, making the right decision time and time again, and watching your numbers."

It's a piece of advice that has been valuable for the Gronkowskis on the football field, and in the office, Dan says: "There are ups and downs [in business]. You can't get to high and you can't get too low, just like in sports. You've got to stay consistent."

Don't miss: A-Rod feels like the sixth 'Gronk' brother after investing in Chris Gronkowski's 'Shark Tank' business

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