One way this is evident in this world is the high number of relapses among people who currently use drugs or the very fact that these drugs do not affect everyone users alike. The model focuses on how drug-related stimuli trigger excessive incentive motivation for drugs, leading to compulsive drug seeking (Vanderschuren & Everitt, 2004), drug taking, and relapse (Robinson & Berridge, 1993). . Simply put, repeated use and exposure to drugs sensitizes the affected pathways and neurons leading to tolerance, implying that there is a decrease in the effect of drugs with repeated administration. Furthermore, incentive sensitization theory provides us with evidence that a major reorganization of the brain's reward systems is possible, meaning that people can develop chemical dependence with drug exposure. First-time users are more likely to have a higher chance of becoming addicted depending on their first encounter with the drug. For example, once an individual consumes their first dose of heroin, each “high” will not be the same as the initial “high,” causing subsequent dosage increases