Most people have their attention decided by a combination of biology and social norms, but can learn to direct it themselves. So if you're really hungry, maybe you can't stop thinking about a sandwich. But most of the time your boss can tell you to pay attention and you will, and you can mediate and think of nothing with practice.
When you have ADHD, your attention can't be controlled by social norms, and the biology of your attention is different. And it's harder to learn to control it yourself. In school, you literally can't pay attention if you don't find the subject interesting, it's too much work. And maybe instead of being hungry and thinking of a sandwich, you'll go on Wikipedia to learn about the history of snail entomology and end up going 10 hours without food or water. The way your attention moves around is dysregulated. That's ADHD. Learning to control your attention is an uphill battle, and you'll never develop a single habit.
That's a pretty high caliber shot to miss the point with