But I also should clarify that this is specifically the basal ganglia that is being affected, and the basal ganglia works in a rigid way. A 'habit' isnt sticking after 50 days, you might be replacing it occasionally with something else, which is essentially breaking the habit. From the book, I can imagine a bunch of ways why this is going wrong.
Maybe you are doing something that scratches the itch that would otherwise drive the habit.
Maybe you are not doing the cue-routine-reward cycle when you do your new habit.
I feel like I'm doing a real disservice to the book because I'm summarizing ~300 pages, I'm about to hop off HN and don't want to go into further detail, and I don't even know what habit you were working on.
Don't let my terrible comment dissuade you. I also don't recommend summaries of this book, they missed too much.
I've done things every day for 50+ days without the habit sticking. I think I heard "habit resistance" is related to ADHD.