People use alcohol and drugs for only one reason, to alter their brain chemistry so that they feel "better" than they did previously. Therefore, without exception, a person who is "under the influence" is suffering from chemically induced abnormal brain function, and is unable accurately to judge her own behavior. That is why so many people swear that they drive better, dance better, think better when high.
The people around them, of course, know the truth of the matter. This truth has been borne out in literally hundreds of experiments all over the world. ( You, of course, are an exception.)The physiology of intoxication and addiction is well-known here at the beginning of the 21st Century. We know that the brain and other organs undergo changes when subjected to the frequent presence of drugs and alcohol. We know that eventual semi-permanent changes occur which cause the victim to be convinced absolutely that s/he cannot exist without the drug(s). This conviction is on the sub-cortical level, based on information interpreted by the primitive portion of the brain. It is not a conscious thought, and is not amenable to reason or education! Only when the person’s life is in such chaos that it presents a greater challenge than living without drugs does the individual become capable of considering change, (the "rock bottom" we hear about.)
It is probably impossible for a person who has not himself been subject to such compulsion to understand it other than in a shallow, intellectual way. It is something that one either believes, because it makes sense and describes an observed reality, or that is disbelieved for whatever reasons -- many of which may bear looking at.
We need to be careful, when we make statements about alcoholics, addicts, and addiction, that we are speaking from empirical knowledge. Addiction has touched virtually every person in the country in one way or another. We all have an emotional stake in the concept. If we are to discern effective ways of dealing with these problems, we need to insure --- to the extent possible -- that we are viewing the subject accurately, rather than "through a glass, darkly."
Here is a link to the National Institute on Alcohol and Alcohol Abuse FAQ page, for a real eye-opener regarding the impact of these problems on society in the US. Fact Sheet