This study examines the nature and origin of a common misconception about moving objects.  We first show through the use of pencil-and-paper problems that many people erroneously believe that an object that is carried by another moving object (e.g., a ball carried by a walking person) will, if dropped, fall to the ground in a straight vertical line.  (In fact, such an object will fall forward in a parabolic arc.)  We then demonstrate that this "straight-down belief" turns up not only on pencil-and-paper problems but also on a problem presented in a concrete, dynamic fashion (Experiment 1) and in a situation in which a subject drops a ball while walking (Experiment 2).  We next consider the origin of the straight-down belief and propose that the belief may stem from a perceptual illusion.  Specifically, we suggest that objects dropped from a moving carrier may be perceived as falling straight down or even backward, when in fact they move forward as they fall.  Experiment 3, in which subjects view computer-generated displays simulating situations in which a carried object is dropped, and Experiment 4, in which subjects view a videotape of a walking person dropping an object, provide data consistent with this "seeing is believing" hypothesis.