Homeless teen to top tennis coach: Jason Stacy's story

To survive, he had to read people's intentions quickly. He learned to understand what others wanted and whether they were safe. That skill now translates directly into his coaching. Professional athletes are surrounded by people who influence them in various ways, Stacy said. His job is to help Sabalenka identify what she needs in a given moment and surround herself with people who can help her get into the right mindset.

A turning point came when he walked into a martial arts center. There he met a family that became his adoptive family. "At the time, I just knew I needed to be around them and their genuine, good intentions," Stacy said.

There was no single moment when he knew he would be OK. Instead, he took small steps: the dojo, the family, becoming a massage therapist, then a sports trainer. "Small consistencies can lead to big change," he said. He wrote a book called "The Pressure Code: How Elite Performers Align their Energy, Emotions, and Environment."

Stacy said his 15-year-old self would not be surprised that he has created a successful life, but he would be proud. "Being aligned with who I am has served me well then and continues to pay off," Stacy said. "I believe that's true for everyone."