Abstract: During the core collapse of a massive star, the formation of the protoneutron star is accompanied by the emission of a significant amount of mass-energy (a few tenths of a Solar mass) in the form of neutrinos. This mass loss generates an outward-propagating pressure wave that steepens into a shock near the stellar surface, potentially powering a weak transient if the core collapse itself does not produce a successful supernovae. I will discuss a general formalism for analyzing this mass-loss-induced shock formation in otherwise-failed supernovae. I will then apply this formalism to polytropic stellar models, and make predictions for the energy contained in the shock as it erupts from the stellar surface. I will show that these predictions are in good agreement with numerical simulations -- both of polytropes and of more general stellar models -- and heuristic estimates. Our findings have important implications for the appearance and detectability of failed supernovae.