At what point does a good habit cross over to the dark side and become a bad habit?

In a nutshell! I wonder where the boundary lies between habit and OCD? 

Hey, Didge...

I suspect the difference lies in the issue of anxiety.  

I floss my teeth by quadrant in a certain progression to make sure I get all of them, but preferably only once per episode.---useful habit.

Flossing again because I was worried that I didn't do a good job the first time would lean toward obsession.

Obsessive-compulsive disorder (OCD) is an anxiety disorder in which people have unwanted and repeated thoughts, feelings, ideas, sensations (obsessions), or behaviors that make them feel driven to do something (compulsions).Often the person carries out the behaviors to get rid of the obsessive thoughts, but this only provides temporary relief. Not performing the obsessive rituals can cause great anxiety. A person's level of OCD can be anywhere from mild to severe...

https://www.psychologytoday.com/conditions/obsessive-compulsive-disorder

Good distinction, Tom. 

I think a habit is something you can stop doing, but OCD is not a conscious thing, so it would be harder to stop.