The person with OCD fears events they are sure will happen if they do not complete an action, several times at least to make sure that there is no possibility of disaster.
Behind most OCD is a far greater anxiety or problem or negative past event that are much to painful to address. The OCD is a lesser anxiety, ( almost acceptable) but a great concern. The person usually realises the behaviour is not usual but are unable to do anything about it.
The behaviour is to a degree addictive as it it reinforced by the completion insuring that no negative event happens. Bit like pavlov's dog. It is in this sense an addictive behaviour but, in my opinion to treat it as such is simplistic. The payback gained by the behaviour has to be reduced and the person ultimately mentally strengthened enough to address the underlying problem.