"It's like if you take everything you think about painting and just throw it out the window," he said. "When you paint your room in your house, there's a wall, you're trying to put thick paint, you're trying to get even strokes. Shoes (are) the exact opposite."
Fourteen years ago, painted a pair of shoes for a girlfriend for Valentine's Day. Twenty hours later, a career was born.
"She loved them, put them on social media," Rivero recalled. "Next thing you know, friends were like 'Hey, my dad's a Yankee fan' or 'My daughter's having an Elmo party.'"
Rivero lives in Miami. A former Dolphins player saw the shoes and, suddenly, business was off and running.
Shohei Ohtani's 50/50 milestone sparks frenzy at Fountain Valley sports store
"An hour before the game I'm getting a phone call and it's Marshawn Lynch," Rivero said, referring to the former Seahawks player known by the nickname "Beast Mode."
"In Marshawn Lynch fashion, speaking as you could imagine, calls me and was like 'Hey, this is Marshawn Lynch.' I was like 'Oh, my God.' Sure enough, I do a whole bunch of shoes. I end up doing a pair for Marshawn that gets us into crazy trouble."
In 14 years, Rivero has customized thousands of shoes for pro athletes across the globe.
"Major League Baseball had a 51/49 rule that stated 51% of the shoe has to be the primary color of the team," Rivero said. "Those rules have now disappeared."
The other "ah-ha" moment was when Shohei Ohtani's representatives called, asking for a shoe for Players' Weekend, showcasing his dog "Decoy."
"It's one of those "oh, man" moments," Rivero said. "They're like 'Make it mostly white, a little blue, but the dog is the focus. So that's what we did -- we put two pictures on the outer ankle bone."
Rivero assumed Ohtaini would simply wear the shoes during Players' Weekend, possibly keeping them or donating them later.
But "the man hasn't taken them off," Rivero said last week.
On Sept. 19, Ohtani wore the signature New Balance shoes as he achieved a remarkable benchmark -- becoming the first player in league history to amass 50 home runs and 50 steals in a single season.
After the game, the shoes were authenticated before being sent to the National Baseball Hall of Fame in Cooperstown, New York, ESPN reported.
And Rivero said he received a call from Ohtani's reps requesting another pair of shoes -- "not to wear but for his house."