ADD is part of a continuum.
Most of us fit on this continuum in that we all have qualities that are common to ADD, but normal forgetfulness, daydreaming and impulsive behaviour are not Attention Deficit Disorder. The key is impairment. It's not that people with ADD can never focus or pay attention. They just can't select when to pay attention, what to pay attention to, and when to stop. While they often fall out of focus in class, at work, or in the middle of conversations, sometimes they get so hyperfocused on things that they forget to take a break.