For a man who considers himself a positive and optimistic fellow, the events of Feb. 8, 2017, shattered Nik Wallenda’s spirit. It even caused him to contemplate something he had rarely considered before: his relationship with fear. The self-proclaimed “King of the High Wire,” Wallenda has 11 Guinness World Records for high-wire acts, all of them sans safety net. A seventh-generation member of the Flying Wallendas and great-grandson of the legendary Karl Wallenda, in the last decade, Nik Wallenda has become known for a series of one-upping-himself TV specials. The list includes being the first person to walk on a tightrope across Niagara Falls in 2012; crossing the Little Colorado River outside Grand Canyon National Park in 2013; walking wires between three Chicago skyscrapers in 2014, including one blindfolded; and walking a 1,300-foot wire atop...