As an employee with ADHD, I found this rather unhelpful. Some of us do have to work for a living, and getting fired can have very serious consequences on our lives. For a lot of us, avoiding (or increasing the likelihood of avoiding) being perceived by our employers as "lazy, careless, unreliable, or defensive" is often worth the exhaustion of trying.
Do you mean you actually work hard or just avoid getting caught being lazy? If you can work hard, I dont think you had an inability to do it in the first place
If you have ADHD, and you need to work for a living; in time, you come up with personal strategies. I found that I am able to focus on things better when I am under a lot of stress or pressure. So I actively try to put myself into these kind of situations. Or, I found that simply sitting down, removing all possible distractions, and consistently forcing myself to do a thing does work; although with severely reduced efficiency i.e. sit down 4 hours, get 1 hour of work done with ~20 internal interruptions. But it does get done.
These are rather exhausting things to be doing all the time. So you always work hard at working. But you don't get consistent results. If you work harder at working, you get less inconsistent results. My point was that its often worth it.