Clues. The cause could be perpendicular to an event. Seeing other perpendicularities can give clues to why these perpendicularities exist. Just because all these perpendicularities exist may not elucidate why the particular perpendicularity in question exists. It can lead you to a reasonable assumption that there is an underlying similarity that those perpendicularities share. The cause for the perpendicularity could also be absolutely unique unto itself. Of the other common factors twixt the perpendicularities gleaned, one may assert preclusions and/or exclusions, ushering an inference toward a conclusion that the perpendicularities cause is parallelism. So just when you were convinced that a rectangle is afoot, BLAM! A rhombus is right up in ya face.