For almost four decades, infrared and collinear (IRC) safety has been the guiding principle for determining which jet observables can be calculated using perturbative QCD.  Now in the LHC era, new jet substructure observables have emerged which are IRC unsafe, yet still calculable using perturbative techniques.  In this talk, I explain the origin of these "Sudakov safe" observables and show how they blur the boundary between perturbative and nonperturbative aspects of QCD.