A few years back, I wanted to start eating steel-cut oatmeal for breakfast. I had high cholesterol. I believed this lifestyle-change would impact it in a beneficial way. If I was right (I was) it would obviate the need for statins.
After languishing in excuses for a while, I decided it was a matter of discipline. I was going to do it. I would eat oatmeal every day for a week.
When I got through my week, I moved the goalpost to one month. Then I changed it to be every weekday without a predetermined end-date.
After a while, I didn't have to remind myself any more. I had changed my morning routine to include the ingestion of this disgusting goop that balanced out my blood chemistry.
Eventually, something deeper changed. Oatmeal stopped being the tool I used to ruin breakfast every morning and just became breakfast.
It's no longer a rule. The fact that it is a habit is almost meaningless, now. It's just part of my frame of reference.
In my mind, the phrase "weekday breakfast" means "seek out plant material to carry cholesterol out of my body". I rely on the habit of eating oatmeal to make this easier and less of a time-waster than it could be but, when I can't find oatmeal, I still typically fulfill the intent by finding something similar.