 Another striking positive consequence of the Generalized Second Law is that it allows one to derive energy conditions in the context of general relativity. An energy condition is, crudely speaking, a relation one demands the properties of matter to satisfy in order to try to capture the idea that “mass-energy should be positive”. Energy conditions play a central and fundamental role in general relativity, since they are needed as assumptions in essentially every deep, major result proven in the last 60 years, especially those pertaining to singularities and black holes (Curiel 2017). One thing that makes them unusual is the fact that, uniquely among the central and fundamental tenets of general relativity, they themselves do not admit of derivation or proof based on other such principles. At least, no such derivations or proofs were known until very recently, when Wall (2010) argued that the Generalized Second Law implies one. There are several problematic aspects to Wall's argument (Curiel 2017), but the mere fact that he was able to produce a prima facie decent one at all is remarkable, showing that the Generalized Second Law may be a very deep physical principle indeed. One, however, may contrarily conclude that the argument shows rather that the Generalized Second Law is a contingent matter, depending sensitively on the kinds of matter fields that actually exist—if matter fields were such as to violate the energy condition Wall argued for, then his argument would show that the Generalized Second Law is not valid. 