 At the same time, philosophers such as Pritchard and Alison Hills hold that understanding does tolerate certain kinds of luck, and in a way that propositional knowledge does not (Pritchard 2010; Hills 2016). They therefore hold that understanding can be partly externally lucky. Thus imagine your environment is filled with misleading information about some event—the fire that destroyed your house, for example. Suppose that only Source X will offer you the truth about the fire—that faulty wiring was the cause—while all of the other sources will offer plausible but mistaken accounts. If you luckily rely on Source X, that source can enable you to understand why the event occurred, even though it cannot generate knowledge about why it occurred, due to the presence of what Pritchard calls “environmental luck”. The upshot, on this view, is that while understanding is compatible with environmental luck, it is not compatible with Gettier luck. They conclude from this that since knowledge is compatible with neither Gettier luck nor environmental luck, understanding is not a species of knowledge.