Alcoholism is a disease that can be brought on by a number of personal, societal, or genetic reasons. Although some people are more susceptible to developing alcohol dependence than others, anyone can become addicted to alcohol.

Memory

People who drink tend to develop a selective memory, remembering the positive aspects of drinking alcohol, which usually occur early in the consumption process, and forgetting the negative effects, usually later in the process. This gives the drinker a positive perception of his alcohol use.

Social Influence

Alcohol use is widely accepted in society and often portrayed favorably in the mass media. This gives alcoholics the perception that frequent alcohol use is "normal," since everyone around them seems to be drinking.

Inhibitions

Some people begin drinking alcohol to loosen up their inhibitions and be less shy or nervous in social situations. This approach is only temporarily masking a person's issues with social anxiety and will ultimately lead to dependence.

Escapism

Many people drink to use the short-term effects of alcohol, like heightened sense of self-esteem and fewer inhibitions, to help them forget about other problems in their life. This approach certainly does not solve the drinker's problems, may even create new problems and will likely cause the drinker to develop dependence.

Social Pressure

Being in an environment where many of your peers excessively drink alcohol can lead others to develop dependence. Peers can provide pressure to drink with them and also contribute to a sense of "normalcy" of alcohol consumption.

Source:

PBSkids.org: Alcohol, Why People Drink

WebMD: Alcohol Abuse Center

TalkRehab.org: Reasons People Drink Alcohol