The Hardest Part of Forming a Habit

I have always thought that the hardest part of achieving a goal is consistency.

Starting something can be easy. You decide you are going to stretch every day, exercise, drink more water, brush your teeth before bed, take your vitamins, or whatever new self-improvement assignment your brain has downloaded this month.

Day one comes with intention. Maybe even excitement. Then you do it again. And again. Eventually, you have done it for 10 days, then 30, maybe 100. Somewhere along the way, it stops feeling like something you are trying to do and starts feeling like something you do.

Then comes one day.

You are tired. You are busy. Something happened. Your brain presents a very reasonable argument: what will happen if I don’t do it just this once?

And logically? Probably nothing. One missed stretch will not undo months of stretching. One missed workout will not erase your fitness. If you did something for 100 days and skipped day 101, you were still consistent 99% of the time.

Excellent. Beautiful. Mathematically very mature.

Except that is not how it works for me.

For me, after a pause or any form of interruption, restarting is always difficult. Not sometimes. Always. A sick day, a busy evening, travel, a weekend, a schedule change, one strange day where the routine does not happen—and suddenly the task goes from “thing I do” to “thing I now have to restart.”

And apparently restarting is a completely different mountain wearing the same hat.

This is where I went looking for research, expecting it to nod politely and say, yes, that makes sense. Instead, one of the best-known real-world habit-formation studies annoyed me personally.

The study followed 96 volunteers who chose an eating, drinking, or activity behaviour and tried to perform it daily in the same context for 12 weeks. The researchers measured automaticity—basically, how much the behaviour started happening with less conscious effort. Among participants whose habit-formation curves could be modelled, the estimated time to reach 95% of their eventual automaticity ranged from 18 to 254 days.

Huge variation. Fair enough.

But then came the line that stared directly into my soul: missing one opportunity did not materially affect habit formation.

Excuse me?

To be clear, I do not think the data is wrong. That is not the point. The study tells us what happened on average, in a particular sample, with particular behaviours, over a particular period.

But it does make me ask: why am I an outlier in this data?

If missing one opportunity should not materially affect habit formation, why does one interruption so often become the doorway through which my entire habit quietly escapes?

Maybe the issue is that we use the word consistency too broadly. Habit research talks about repeated behaviour in stable contexts gradually becoming more automatic; habits are not literally streak counters, and one missed day does not magically erase all the repetition before it.

But my problem is not always maintaining the behaviour while the routine is intact. My problem is returning after the routine has been interrupted.

Those are not the same skill.

Continuing a moving train is one thing. Restarting the train after it has stopped in the middle of nowhere with no announcement from the driver? Completely different nonsense.

Naturally, I wondered whether this was an AuDHD thing. It would be very easy to build a satisfying explanation using all the familiar words: ADHD, executive dysfunction, autistic inertia, dopamine, monotropism, all-or-nothing thinking. Throw them into a bowl, add a little internet confidence, and suddenly I have a theory that feels correct.

But a satisfying explanation is not automatically an evidence-based one.

A 2026 scoping review on routines and habits in people with ADHD found that the research is still limited: only 31 studies met the criteria, 27 focused on children, and the main areas studied were sleep, feeding, physical activity, and sedentary behaviour. The review also found no validated assessment specifically designed to measure routines or habits in people with ADHD.

So yes, ADHD can clearly affect routines and daily functioning. But I cannot honestly claim, “ADHD people lose habits when they miss one day.” The research does not let me say that.

Autism makes the question even more complicated. One recognized autistic pattern is insistence on sameness, which can involve inflexible adherence to routines, distress at small changes, difficulty with transitions, and rigid thinking.

So should routine be easier for autistic people? Maybe in some ways.

But having a strong need for routine is not the same as being good at deliberately creating, maintaining, and restarting whatever healthy routine you choose. Those are different things.

I may become very comfortable with every night I do X because the predictability removes the decision. Tonight is an X night. Tomorrow is an X night. Every night is an X night.

But when something interrupts it, tomorrow is no longer just another repetition. Tomorrow contains a decision: are we doing X again?

And decisions are where routines go to get mugged.

This is why the 80% rule makes sense to me mathematically and still sometimes fails me practically. If I stretch six days this week instead of seven, that is good. If I exercise 24 days out of 30, that is excellent. My body does not throw the successful days into the garbage because I missed one.

But the problem for me is not the missed 20%. The problem is what happens afterward.

Some people seem able to say, Didn’t do it Tuesday. Anyway, Wednesday… and continue.

For me, Tuesday can become a hole in the road.

Maybe consistency is not one skill. Maybe it is at least three: starting, maintaining, and returning.

Can I begin the behaviour? Can I keep repeating it? Can I resume it after life interrupts it?

I have treated those as one ability for years, but maybe they are not. Maybe someone can be good at maintaining and terrible at returning. That would explain a lot about me, honestly. I can keep some things going surprisingly well—until I stop. Then beginning again feels harder than continuing ever did.

So maybe the useful question is not, how do I become someone who never misses a day?

That sounds exhausting and also fake. Life will interrupt every routine eventually. Illness, work, travel, children, exhaustion, random chaos, general life. A system that only works when nothing interrupts it is not resilient.

Maybe the real skill I need is not perfect consistency. Maybe it is boring recovery.

Miss day 101, and day 102 is not a dramatic moral event. No guilt. No punishment. No restarting the whole counter. No waiting until Monday.

Just: oh. We are doing this again.

I do not have a neat conclusion yet, which is partly why I am writing this. I am curious where other people fall on this.

If you have done something consistently for months and then miss one day, is the next day simply another day? Or do you recognize this weird transition where stopping once somehow makes stopping again dramatically easier?

And if you are autistic, ADHD, both, or neither—does that change your experience?

Because the data does not say I am wrong. It just makes me wonder why I am sitting in the weird corner of the graph, waving politely, unable to restart after one missed day like a normal software update.