For obsessive compulsive disorder (OCD), the most familiar example should be hand washing. For this group of patients, they constantly feel that their hands are dirty and hence wash it over and over again. The patients actually realized that their hands are not dirty but the obsessional thoughts repeated intrude their thoughts. The more the patients try to stop the thoughts, the more powerful and unstoppable the thoughts become. Consequently, the act of hand washing is used to relieve the stress from the thoughts. After the act of hand washing, the patients may feel relieved but the problem remained unsolved. The intrusive thoughts keep on coming and hand washing acts need to be repeated and the vicious cycle continues.
Some would have the ritual of checking the door lock repeatedly despite knowing that the door was securely locked behind them. The thoughts stir their mind and the checking ritual reduces the anxiety and insecurity in them. The common types of compulsive behaviours include hand washing, checking locks, bathing, swallowing of saliva etc. Patients with OCD are forced to perform these acts in order to reduce their level of anxiety.