It seems to me that managers who make "impossible" demands that flout reality believe, in their heads, that they're in some kind of negotiation. They may fully

It seems to me that managers who make "impossible" demands that flout reality believe, in their heads, that they're in some kind of negotiation. They may fully realize that what they're demanding is impossible but feel that by making the demand, it will force a greater sense of urgency and thus "speed up" delivery. There's another, perhaps more insidious, variant of this when managers ask YOU "How long will X take?" It's often asked casually. But your answer, which you think reciprocates the casual-ness, is then taken as a hard deadline regardless whatever surprises pop up (even if the manager knows there's going to be curveballs). Failure to meet the deadline is then fully your responsibility. It's something that everyone learns sooner or later in their careers-- to not make casual estimates, EVER.