Obsessive Compulsive Disorder, which is characterized by persistent thoughts, impulses, or images (obsessions) and repetitive stereotyped actions (compulsions), has always been a disorder that I found to appear frightening, yet interesting. I had watched a documentary on it on television years ago, and was saddened that, as with many psychological disorders, those suffering from this can be trapped within an individual prison their own mind has created. Feeling compelled to carry out irrational actions, and ruminate over obsessive thoughts can be entirely debilitating for those individuals suffering.
I found that it was interesting that the book mentioned that cleaning and checking (making sure the stove is off/that the door is locked) were two of the most common forms of compulsive behavior. Both of these things can serve a great purpose in survival, such as avoiding deadly bacteria and making sure your shelter is not in ashes when you return. It seems as if these instincts for protection get heightened and go into overdrive when accompanied by stress which then feeds the obsessions and encourages rumination. It is great that Exposure Response and Prevention is successful in treating those with this disorder, and help to better understand more about its possible origins. I think more people are on the "spectrum" of OCD, without even realizing it.