WHEN WE SUBMIT to the temptation of achieving pleasure and instant gratification, it comes at a personal cost. When we find ourselves compromising our morals, principles, careers, goals, family, and health to achieve that "feel good" moment--and find ourselves doing so over and over again--we can start talking about addiction.
It is in human nature and design to seek out what is most pleasurable, enjoyable, and least difficult; only when we are following a greater purpose to achieve our goals do we choose to take a more-difficult path. We all long for pleasure and, the faster and easier we can obtain it, the more we risk becoming addicted to the source of pleasure. The design of the human mind allows us to experience enjoyment, but also makes us vulnerable to becoming addicted to these pleasurable experiences.
Our brain is designed intelligently. The circuitry--the dopamine reward pathways--helps us enjoy pleasurable activities, such as great meals, good company with friends, or a stimulating encounter with a new romantic interest. These pathways encourage us to seek out exciting and pleasurable experiences, and reinforce these types of behaviors when we seek them out, making us more likely to do so over time. Let us underscore that there are survival reasons to this reward system: food is pleasurable to encourage us to eat and stay alive; sex is pleasurable to encourage us to mate and reproduce.
The reward system is first stimulated when an addictive substance or pleasurable experience is encountered. Practically all addictive substances will--directly or indirectly--increase dopamine levels in your brain. Dopamine is a neurotransmitting chemical that is involved in pleasure and motivation.
When exposed to an addictive substance, the reward circuitry stimulates some people to seek more-intense experiences to achieve the same pleasure. As someone repetitively uses the drug, dopamine is released, but the brain becomes "used to" the dopamine, and so releases less dopamine for the same amount of stimulation (or same amount of substance), and therefore requires ever larger amounts of stimulation to achieve the same pleasure as time progresses.