Addiction often begins with the voluntary use of a substance, such as drugs or alcohol, that provides a sense of pleasure or relief. Over time, repeated use can lead to changes in the brain's reward system, making it increasingly difficult to feel pleasure without the substance or behavior. These brain changes can affect a person's ability to make decisions, control impulses, and manage stress, leading to a cycle of dependence and compulsive use. Factors such as genetics, environment, mental health, and early exposure can also contribute to the development of addiction.