It is easy to see why people would want an answer to “why.” In our society, we can go to the doctor to get medication or surgery for numerous problems that afflict us. If we have an infection, we take an antibiotic. If we have a tumor, we remove it and follow that with radiation and chemotherapy. If we have a headache, we take a pain reliever, and the pain subsides. Further, we can attribute a cause to many of these problems, such as bacteria causing an infection, smoking leading to the development of a lung cancer, and a head injury leading to a headache.
With mental disorders, we cannot be that precise because the brain is the most complex thing in the known universe. We are just beginning to understand how it works and functions. We are nowhere near the level of sophistication of being able to say that one experience led to the development of a disorder. The reason for this is simple, if an environmental experience did lead to the development of a disorder, then every person that experienced that environment would develop the disorder, and this simply does not happen. Therefore, it is the interaction of our environment and our brain (back to nature and nurture) that leads to the development of disorders, and therefore to OCD. Can specific experiences lead to the development of OCD in a specific person? Of course, but is that experience going to lead to the development of OCD in every person? No.