How we become addicted

 Reward system is an area of brain where if you do a certain activity that brain area feels pleasure in that and you feel a sensation of being of feeling good and that is why brain has this tendency of repeating that action which makes you feel good that term is called addiction.

It is also a basis of habit formation , whatever you feel go to tend to keep doing again and again on the basis of it is feeling good inside in this reward system.