Why can patients with ADHD control their behavior in some but not all circumstances?

Patients with attention deficit hyperactivity disorder (ADHD) can be quite impulsive, restless and easily distracted. In short, they often have difficulty controlling their behavior. Diminished behavioural control can result in problems at work or in someone’s social life. Although patients with ADHD often find it hard to focus at work, some can spend hours playing computer games without facing distraction. In other words, patients with ADHD appear able to control their behavior much better when they are doing something enjoyable or rewarding rather than boring.