Under Armour recently surpassed Adidas in sales to become the number two sports apparel company in the U.S., trailing only Nike. But founder and CEO Kevin Plank has made it clear he has no intentions to stop there.

The challenge now is to stay nimble and pursue the kinds of innovations that will take the company to the next level--not an easy task when you have 15,000 employees spread across 26 offices. Speaking at the Fast Company Innovation Festival in New York City on Thursday, the entrepreneur revealed the kind of attitude Under Armour won't tolerate from workers.

"The only thing that will get you fired here," Plank said, "is to say, 'But, that's the way we've always done it.' "

Plank might be exaggerating, but the ethos helps explain some of the big investments the company has made recently in an effort to propel Under Armour into the future.

The company has an uphill fight against Nike--its projected $5 billion in revenue this year is just a fraction of the larger company's expected $33.9 billion. One of the ways Under Armour, which Plank founded in 1995, is trying to make up that ground is by creating sports apparel that combines wearability with tech. Over the past three years, the company has spent nearly $1 billion acquiring health apps like MapMyRun that can track workouts and monitor nutrition. Plank has said the company wants to incorporate those technologies directly into its clothing, creating apparel that lets athletes track their health in real time.

In June, Under Armour opened the Lighthouse, a 35,000-square-foot innovation lab near the company's Baltimore headquarters. There, it's using some of the most advanced tactics around to manufacture its clothing: a machine that automatically cuts sheets of fabric so as to produce the least amount of waste possible; 3-D body scanners that let it create customized clothing for top athletes.

The Lighthouse is also where the company makes its Architech, a partially 3-D printed sneaker that retails for $300. Robots can make 2,400 of the shoes in eight hours, a task that would usually require 200 humans. Those shoes quickly sold out after they launched in July.

Some investors have responded to Plank's investments with skepticism. Under Armour's stock is down about 20 percent over the past 12 months. It recently took its biggest single-day tumble in nearly eight years after Plank warned that the company's margins wouldn't be as high as they have been in recent years. Plank noted on Thursday that Under Armour has maintained 20 percent revenue growth in 26 consecutive quarters--the only consumer company on the S&P 500 that can make that claim--and is still on pace to reach $7.5 billion in revenue in 2018.

At Thursday's event, Plank was sharing a stage with golfer Jordan Spieth, who won the 2015 Masters and U.S. Open at the age of 22. On the final day of the Masters, Spieth, who signed with Under Armour in 2013, took a risky shot on the notoriously difficult 13th hole despite having a lead at the time. The risk paid off--Spieth made the shot of his life and went on to win the tournament by four strokes.

"I trusted myself, and I bet on myself. I didn't need to back off and play it safe," Spieth said. "As a pro golfer, you're financially set even if you don't win. But I'm stubborn. I want to be the best. I want to be remembered for how I play the game."

Plank says that this is the type of mindset Under Armour looks for in its athletes--a list that also includes Michael Phelps, Steph Curry, Lyndsey Vonn, and Bryce Harper--as well as its employees.

"We want them aggressive and fearless," Plank said. "That creates a certain culture. That attitude is in our DNA."