Obsessions cause anxiety. Anxiety is the reason why you start doing compulsions. You want to relieve the anxiety and, in the beginning, doing compulsions seems like a good way to relieve anxiety. But after a point, the compulsions do not seem to relieve the anxiety as well as they did earlier, getting you to do compulsions more frequently in every instance as well as more instances of it.
Think of an alcoholic who has taken to drinking to combat stress. When he first drinks, it may have been to relieve work stress, and a couple of drinks may have been sufficient. When that ‘helps’ relieve work stress, he may start drinking to relieve other types of stress as well. If he fights with his wife, he may end up drinking. If he loses some money in gambling, he may end up drinking. Even if he feels good about himself, he may end up drinking to celebrate. On every occasion, the number of drinks may not be restricted to just two but may gradually keep increasing. Slowly, he may get so used to using alcohol to cope that he may need a few drinks to just face a normal day. Soon, he may need to engage in pre-emptive drinking to avoid all stressors, whether they exist or not.
In the same way, you may fall back upon pre-emptive compulsions to help you deal with the potential anxiety that Harm OCD triggers may cause. When the obsessions become more difficult to bear, you may begin to identify the cues that are likely to cause you anxiety and begin to avoid them. So, you may stay away from tools, sharp objects and people too for fear of harming them. Handling the tools around people may not cause as much anxiety as the thought of becoming anxious when you handle the tools may. This anxiety is in anticipation of being triggered. This anxiety is anticipatory anxiety.
Alternatively, when you begin to recover from your Harm OCD, obsessions that caused you immense distress earlier do not do so any longer. When this happens, this may seem scary too because you do not feel the familiar physical manifestations of your anxiety. It may cause a mixed feeling. You may be on the one hand relieved that the obsession is not causing you anxiety. But on the other hand, it may seem like a time bomb waiting to explode and you may become anxious about eventually feeling more anxious than ever. Thus, even though the obsession does not cause the anxiety anymore, not becoming anxious when triggered may cause anxiety. This is also anticipatory anxiety.
Anticipatory anxiety may cause avoidance, and avoidance becomes the compulsion. You may take great pains to not have an encounter with the dreaded stimulus, because of the fear of the anxiety that it may cause. The problem with avoidance, as we know is that it causes a magnification of the problem and an overestimation of the intensity of the likely anxiety that facing the stimulus will cause. The longer the avoidance, the larger the problem seems to become.
When you start facing the stimulus that is the cause of the anticipatory anxiety (by avoiding avoidance), you may realize that the anxiety of facing the stimulus is probably lesser than it was in your mind. So, you might think that going on a double date may be a 9 on the SUDS, but when you do go for the double date, you may find your anxiety to be a 5 or a 6 on SUDS. You may be able to use this knowledge to boost your confidence and do more exposures to get over this fear altogether.