Because according to the manual doctors use to diagnose ADHD, the symptoms can be broken into two categories: one called hyperactivity-impulsivity... and one called inattention.
For example, one of the more frequently debated conditions is Attention Deficit, Hyperactivity Disorder or ADHD, a condition marked by an ongoing pattern of inattention or hyperactivity and impulsive behavior.
Four weeks passed away, and Jane saw nothing of him. She endeavoured to persuade herself that she did not regret it; but she could no longer be blind to Miss Bingley's inattention.
This was quite a new idea to Mrs. Dashwood; she had never been used to find wit in the inattention of any one, and could not help looking with surprise at them both.