"At such moments the collapse of their courage, willpower, an..." — Camus Albert quote meaning

At such moments the collapse of their courage, willpower, and endurance was so abrupt that they felt they could never drag themselves out of the pit of despond into which they had fallen. Therefore they forced themselves never to think about the problematic day of escape, to cease looking to the future, and always to keep, so to speak, their eyes fixed on the ground at their feet. But, naturally enough, this prudence, this habit of feinting with their predicament and refusing to put up a fight, was ill rewarded. For, while averting that revulsion which they found so unbearable, they also deprived themselves of those redeeming moments, frequent enough when all is told, when by conjuring up pictures of a reunion to be, they could forget about the plague. Thus, in a middle course between these heights and depths, they drifted through life rather than lived, the prey of aimless days and sterile memories, like wandering shadows that could have acquired substance only by consenting to root themselves in the solid earth of their distress.