Some habits are more fragile than others.
Once established, some habits are very delicate. If you miss a day or try to alter them, it’s easy to knock them out of place completely and see them fade out.
Other habits are more resilient. You can push and prod them, change them in different ways, and they still stick pretty well. At the extreme they act like borderline addictions – it’s harder to stop doing them than to keep doing them.