The onset of breakup of liquid jets or sheets is commonly predicted by determining bow infinitesimal disturbances grow with time. This theory is usually called temporal theory. A more recently developed theory predicts bow a disturbance evolves in space and time. The latter theory is termed spatiotemporal theory. This article demonstrates how temporal theory may mispredict the nature of the onset of instability. A very important type of instability called absolute instability also totally escaped the prediction of temporal theory. The misprediction and the incompleteness of the temporal theory is demonstrated by use of an example of sheet breakup preceding the atomization.