Addiction is something that causes us to keep coming back for more of something. We can become addicted to good things, or bad things, but typically an addiction is never a good thing. Instead, we should learn to do things in moderation.
Addiction is caused by the body's natural response to enjoying something. Our brains are programmed to release dopamine when we enjoy something, which is a chemical that gives us that ‘feel good' feeling.
In a normal circumstance, the effects of dopamine are temporary. When you become addicted to something, the dopamine effects can last much longer due to the body's inability to re-absorb the dopamine back into its system, and as a result, the body adjusts the amount of dopamine that is released at one time. This explains why a high may seem to become less and less effective over time with an addiction problem.