My personal experience is that the cost of enduring a negative stimulus is not simply a function of the magnitude of the negative stimulus, but rather the magnitude of the negative stimulus in relation to the magnitude of all other concurrent negative stimuli. This study controls the environment so that a single negative stimulus is isolated and additional external negative stimuli are minimized, but it cannot control for the fact that a depressed person also endures a constant barrage of negative stimuli which are generated internally (hopelessness, exhaustion, fear, self-doubt, etc). The magnitude of these internally generated negative stimuli is likely much larger than that of the aversive external stimulus used in this study, so it seems reasonable that the marginal relief obtained by avoiding the external stimulus may be perceived as relatively negligible, or at least diminished to the point that the cost of avoiding is greater than the cost of enduring.