In photography, the aperture is the opening in a lens through which light passes to enter the camera. One of the critical effects of the aperture is something known as depth of field. A wide open aperture results in shallow depth of field, which leaves the background of an image blurry. A small aperture ensures both foreground and background remain in sharp focus.
Aperture is a metaphor for the role of the consultant. While the client might identify the subject on which to focus their lens, an effective consultant should control the depth of field. At times the consultant should bring the background landscape into full focus for broader context, while at other times that background noise should fade to not distract from the foreground subject.