I never thought about it that way - but it makes sense.
Take Depression - we all get a little sad, but Depression takes that sadness to a point where we can't escape it. THAT'S the part that's not normal.
You mentioned OCD in your article, at some point we all get a little obsessive about something - we just call it a hobby or interest. It is when we can't turn our focus to anything else that it becomes a disease.