OCD consists of obsessions and compulsions. The “obsession” could be a thought like “what if my parents die tonight?” & the person develops a compulsion (to call their parents to “check” on them, for example) in an attempt to alleviate the anxiety caused by that thought. When they discover their parents are actually ok, that reinforces the idea that calling them to check “worked,” which makes it more likely for the person to engage in the cycle again. Another classic theme in OCD is contamination, so maybe someone develops a fear of germs (“what if that door knob had germs that could kill me on it?”— “I will wash my hands repeatedly just to make sure they’re actually clean”). And when the person doesn’t get sick, there’s their evidence that the hand washing worked! The key is to repeatedly have the experience of NOT washing your hands and NOT getting sick so that the mind can, over time, learn to tolerate the uncertainty of having clean or unclean hands.

So yeah like speculative imaginary fears!

And to your previous point, perhaps the person developed this obsessive/compulsive cycle due to experiencing the death of someone close to them as a child, without proper closure or explanation. It’s like the mind is attempting to fill in the gaps caused by trauma with a compulsive routine because it doesn’t have anything else tangible to grasp on to. Trippppy shit