AS THE PARENT OF A 14-YEAR-OLD SON AND A 2-YEAR-OLD DAUGHTER, I spend a lot of time thinking about risks. Liam says he expects to take the Red Line to school in the fall and that he wants to shoot his grandfather’s guns when he visits Kentucky soon. Ruby fights when I hold her hand crossing the street and cries “Self!” when I try to steady her at the top of the twisty slide. It is remarkable how often my heart is in my throat.

 But I don’t think I’ve ever been more scared than I was this summer, standing with Liam at the top of a cliff in Italy. Every few years we go on a big hiking trip, and this time we were trying an “iron way,” paths in the Dolomite range that have steel cables bolted into the rock face. The cables offer a secure handhold while your feet seek purchase on the narrow paths. The system allows access to trails only mountaineers could otherwise negotiate.