I think the definition of 'luck' as 'complex outcomes I have only minor control over' is useful, as well as the definition of 'luck' as 'the resolution of uncertain outcomes.' For both of them, I think there's meat to the sentence "rationalists should not be predictably unlucky": in the first, it means rationalists should exert a level of effort justified by the system they're dealing with, and not be dissuaded by statistically insignificant feedback; in the second, it means rationalists should be calibrated (and so P_10 or worse events happen to them 10% of the time, i.e. rationalists are not surprised that they lose money at the casino).