"I said, 'Duuuude!' " Kotsenburg, 20, recalled of the conversation with his older brother. "And he's like 'Whaaaaaaaat?' "
Whatever it was that pushed him to the performance of his young and unconventional life, suffice to say, it can't be bottled.
The goateed Kotsenburg, his long, blond hair waving like a rebel flag, nailed one spinning, flipping, twisting trick after another at gorgeous Rosa Khutor Extreme Park to became the Sochi Games' first champion.
In the remaining two weeks of these 2014 Winter Olympics there will not be a more unusual one.
"Felt great to be reppin' the U.S.A.," he said after capturing his nation's first medal.
In an event some competitors felt was tainted by superstar Shaun White's withdrawal Tuesday, Norway's Staale Sandbech took silver and Canada's Mark McMorris the bronze.
Some of McMorris' Canadian teammates had been critical of White, saying that after the two-time half-pipe gold-medalist saw the difficult course he opted to withdraw with a slightly injured wrist and focus instead on his pet event.
"It kind of [stinks] that Shaun wasn't there," said Kotsenburg. "But it's kind of cool, too, because people were like: 'Whoa, there's other snowboarders?'
"But he's going to go in his other event, and I'm sure he's going to rock it."
That's exactly what Kotsenburg did on a blue-sky postcard day in the mountains north of Sochi. After qualifying for the second and final run, he posted a score of 93.50 with a trick he invented. The 91.75 Sandbech received from the panel of judges was the closest anyone came.
It was while waiting at the top of the hill before that fateful run that Kotsenburg, third after the initial round, phoned his brother back home in Park City.
Blaze, 22, urged Sage to try the new jump he'd been practicing for months - the one the snowboarder had dubbed the back 1620 Japan air.
The 1620 is the number of degrees he spins - 41/2 twists - while further contorting himself and grabbing the back of his board.
"I invented it a couple of months ago," he said. "It was really cool to do it here. . . . That was the best run of my life, hands down."
Having skipped the opening ceremonies and slept well for the first time since arriving here, Kotsenburg felt unusually refreshed and relaxed Saturday. Some of that he attributed to the fact that his family stayed home.
"They stress me out way too much, dude," he said, "so I was like, 'Hey, why don't you guys just hang out at home?' I try to put everything out of my mind. I ride really bad when I start overthinking."
He stood at the top of the course - steeper and more treacherous than almost any these daredevils encounter, with its daunting series of rails, ramps, and hills - and admired some of Russia's natural, high-altitude splendor.
"It was awesome scenery," he said.
That course, on which White and several others had fallen hard during practices this past week, had been criticized as too dangerous. Not by Kotsenburg.
"I was down with it," he said. "We need these big jumps to do the tricks we do. I don't think I would have won without them."
Making his way downhill, he kept envisioning his friends at the finish line, wondering what they thought about him landing the daring jump he'd concocted.
"Before you [start], you can't see the bottom," he said. "And when you finally get there and see all the people there, all your friends, dude, it's an awesome feeling."
He called his parents immediately after his triumph, and the conversation with his father, a real estate salesman and clearly a man of few words, was eerily like the one he'd had earlier with his brother.
"I'm like, 'Dad!' and he's like, 'Whaaaaaaaat?' "
Kotsenburg was glad that his event was this Olympics' first. Sitting around his apartment and watching everyone else compete, no matter how many snacks he consumed or movies he saw, would have been torture.
"My mentality [between races] is not going to the gym and making myself better," he said. "I really just like riding and expressing myself."
Now he can relax, breathe in that clear mountain air, and, no matter the sport, watch his American teammates try to emulate him.
"I'm down with watching anything at all," he said. "Hey, I'm at the Olympics, dude."