Jason Stacy coaches Aryna Sabalenka, who is playing in the US Open. Courtesy of Jason Stacy Jason Stacy is a performance coach who helps Sabalenka train physically and mentally. He's also a dad of four, and he aims to teach his kids the same things he coaches. He draws on skills like reading people and staying true to himself. This as-told-to essay is based on a conversation with Jason Stacy, author of "The Pressure Code: How Elite Performers Align their Energy, Emotions, and Environment." ...