Although having, generally the same meaning, 'behind the curve', at least in aviation, describes a condition in which one has to lower. the nose of the aircraft to climb. The cause is flying at such a low airspeed with a lot of drag, usually produced by the addition of too much flap and with the landing gear down, that the engine(s) is incapable of producing sufficient power to make the aircraft climb. The nose is lowered, the grag is reduced or eliminated and the aircraft will then gain speed and climb. This condition is termed being behind the power curve. This can, as Q rightly observes, be plotted on a linear x, y axis graph...