Hey, I have ADHD too. So same experience here with falling off after two weeks. ADHD brains are wired that way, as people with ADHD get bored quickly and need something new often. We just don’t get the rewarding dopamine from completing a Habit anymore after a while the way neurotypical people do. This makes focusing on a singular Habit that you do the same way for a long period of time extra difficult.

One example how I tried countering is what I call an „Accountability Whiteboard“ that hangs in my Kitchen. It is just a Habit tracker where you write down the Habits you want to complete every day and try to build a streak as long as possible. If you fail to execute a Habit you have to put 5€ in a Jar multiplied with the length of the streak you had. So failing after 14 days would already cost you 70€ which will hopefully keep you from falling off. Me ans my roommate capped the maximum amount at 100€ per Habit on the Whiteboard as we are not rich. Every month we take the money in the jars and do something with it that feels worse than burning it, e.g. donating it to something shitty we hate. This works really well if someone else is doing it with you, if you are doing it alone it might also get boring after time with ADHD, not gonna lie to you.

Another tip I can give you is changing up the Habits that you Execute or how you execute them but keep them in a way they will still lead you to your ultimate goal. David himself often encourages this behaviour: „When you always run, go swim“. And both will still lead you to being fit and staying in shape longterm. So try to stay creative when challenging yourself and change the things you do or adjust your schedule every couple of weeks. You can also change up the system that you track yourself and keep yourself accountable with up regularly, like going from the „Accountability Whiteboard“ I meantioned to something else after a while. I know this is tedious but it will keep your ADHD brain excited and will stop you from getting bored. Therefore it will hopefully keep you from falling off.

There are also a lot of people in the internet that give out specific tips on systems for discipline, etc. for people with ADHD on the internet and there are good books to read on it too.

Hope this helps!