Efficiency measurement has become a very popular field in applied economics in recent years, and with this interest there has been a large intellectual investment in refining the empirical methods available to researchers in the area. In this paper we relate these developments to Harvey Leibenstein's original 1966 insight into the psychological ideas underlying the notion that economic agents may not achieve maximal efficiency in their productive decisions and behaviour. Of course, it is always possible to argue that apparent inefficiency only arises from a failure of the observer to realise what it is that is being maximized. However, we evade this easy escape route into non-falsifiable hypothesizing, and instead take at face value the fact that too many empirical studies have come up with substantial measures of inefficiency for us to ignore its importance for normative economics.