Why do people get obsessed?

Obsession can be caused by lack of confidence / low self esteem. That's when you become unsure of yourself and need something to hold onto that gives you comfort in some way. In come cases, it is linked to a specific fear, like fear of germs can trigger obsessive hand-washing. If you repeatedly go back to check that the doors and Windows are locked before you leave the house, you do not trust yourself to do it right the first time. Building your confidence and self esteem will help drastically to improve an obsessiive disorder.