From your own internal (subjective) experience OCD arises as a phenomena, it is made. The making happens within a few fractions of a second. It seems to not have internal causes when perception of it comes after it forms. It "just happens to you." Causes are seen when perception watches OCD arising as a phenomena. There are "acts" of relating to arising, habits of relating, that are part of what makes it. An impulse comes up with little mental narrative, it is engaged with in some way, a meaning grows, which is engaged with again causing the meaning to grow more and seem intrinsic to the impulse.

i used to count under my breath when i was a kid, "one, two, three, four, five, six, seven... one, two, three, four, five, six, seven..." i find i can be compelled to seek attention, or compelled to anger. These things seem "just to happen to me." But when i look more closely i see an impulse rise up, i see that i relate to it in roughly one of three ways: either i grab it, i resist it, or i lean into it a little with a mild interest. Depending on which way i relate there is a predictable cascade of other internal "acts" like judgement, assigning meaning, and projecting, leaving me in the grips of full blown anger, for example. When i perceive an impulse arising in real time prior to the cascade it does not overwhelm and dictate to me. Further along the cascade i can only cope, through deep breathing for instance, or counting to ten. Even further along the cascade my behavior is being dictated by the previous chain of "acts." The original impulse can be something as quiet as "i want to be heard." It is an open question whether that quiet little voice is attempting to talk to the external world at all, or is in fact simply attempting to talk with me about my own relationship to it. It is an open question whether those little impulses are attempting to tell me anything about the external world at all, or are in fact simply attempting to tell me something about my internal world... Yet full blown anger tends to assume that it is about the world or some part of it, and so it assumes it is for the world, or some part of it. In any given case that may be an error.