Addiction to drugs and/or alcohol is a mental illness. Addicts/Alcoholics live in denial, refusing to connect their actions to the results.
If you give a drunk on the corner $5 for food, he'll go buy beer. By the time they end up on the streets, beer is all they can afford, and in truth, beer is addictive, has as much alcohol as a shot of bourbon--and the alcohol in all drinks is ethanol. Wrecks brain cells.
A terrible downward spiral. I don't think anyone grows up wanting to be a street person.