Orginalny
This varies from person to person, and may even change over time for any individual.
OCD is characterized by obsessions related to fears (e.g., fear of harming someone, fear of contamination, fear of being crazy- there are MANY more) and compulsions or rituals performed to temporarily counteract the anxiety induced by these fears (e.g., checking, hand washing, counting- again, there are many more).
People with OCD recognize that their symptoms (their obsessions, their compulsions) are unreasonable, but they may/may not understand that they are, at least contextually, irrelevant. Perhaps a universal characteristic of OCD that actually gives rise to the symptoms is more important, and that is difficulty accepting:
1.) uncertainty (an inevitable aspect of, well, everything), which in turn allows doubt to take over, and
2.) possibilities of scenarios that are inconsistent with one's held values, beliefs, identity, etc., which can lead to guilt and shame. These inconsistencies may actually just be uncertainty as well...
For example, you hold the belief that you are a good person, but you're a cognitive miser (as we all are) and seek to know for certain that you are a good person. The issue is that being a "good person" is just a label that your mind has categorized; there is no universal definition or it. So uncertainty arrives and tortures you, the cognitive miser. In an effort to combat uncertainty and ensure that you are indeed a good person, you check that you did not cause harm to someone accidentally. Because if you caused harm to someone, either A.) you would not be a good person, or B.) your categorization of "good person" has errors -- and uncertainties. But If A is true, your previously held beliefs about yourself have errors -- also uncertainties. The cognitive miser in you can either prove that A and B are untrue (for now) by checking to making sure that you did not cause harm to someone, or, it can accept the uncertainty and possible errors and just move on and live. We are all cognitive misers, but the OCD's are all the former, wishing we could be the latter.
In my personal experience, the worst part of dealing with OCD is not a specific symptom, obsession, or compulsion. Rather, it's the frustrating inconsistency (for lack of a better word) between:
1.) My overwhelming desire to adhere to the logical, 99.99% of my consciousness: my declarative knowledge that my obsessions and compulsions are unreasonable and unproductive, and
2.) The urges, sensations, emotions, and thoughts that cling to the other .01%: the "but, what if?".