SAN FRANCISCO, Sept. 14, 2015 /PRNewswire-USNewswire/ -- Hidden Strengths: Unleashing The Crucial Leadership Skills You Already Have, is the new book by Thuy Sindell and Milo Sindell, principals at Skyline Group International, a leadership performance company. Every person who is a leader or aspires to be one can no longer depend on what they do well today. The world no longer allows anyone to rest on yesterday's strengths. Hidden Strengths, provides a powerful methodology for continual self-driven leadership development and employee performance.