Gateway drugs lower inhibitions setting the stage for when someone brings out the harder drugs. Once their inhibitions are lowered, people do what they wouldn't ordinarily do. Those vulnerable to depression, anxiety and intense restlessness due to a Chemical imbalance in the brain may self-medicate with Illegal drugs if they don't know or have access to a Doctor for treatment. Unfortunately, there is still a great lack of knowledge on the part of those who suffer and those who treat underlying mood or anxiety syndrome. Many drug abusers are driven by an underlying and often treatable psychiatric disorder.
Stimulants have a paradoxical calming effect.
Everyone is unique as to individual uptake and chemical effect on the brain. Sensitivity and degree of brain damage also play a part. When someone tells you they knew someone who quit so therefore anyone can, they need to get educated to the facts. Victims of chemical addiction need chemical therapy to interrupt craving and the suicidal danger of dysphoria which sets in during withdrawal. No magic talk can succeed where a chemical addiction exists.