When you are clicking portrait images, you can observe that the backgrounds are soft, out of focus and unclear. The background becomes dull and unclear to highlight the subject, so get rid of distraction in the background.
Many aperture photographers, who set the camera in auto mode for portraits and click the images, face the shallow depth problem.
Auto mode does not create clear background in portrait modes and hence many apprentice photographers face this problem.
Portraits are pictures which should eliminate the background and focus on the subject only, but picture without background is awkward.
With small adjustments in the digital camera, you can overcome shallow depth in the portrait and get great portraits [Selecting best digital camera].