Consider the following situation. A man goes to Atlantic City and loses money at various games -- slots, black jack, etc. He enjoys it and becomes determined to improve his performance. Living a distance from Atlantic City, he finds other outlets for gambling. He bets with colleagues at work on football games and other sports events. He goes to the race track. He involves himself with various forms of on-line gambling. Eventually, it seems that gambling dominates his life. He thinks about it when not engaged in it. Anytime he travels, he locates in advance any casino in the vicinity. Then he starts taking time off from work to gamble. He does not tell his family about these activities. Gambling has become the most exciting thing in his life. He starts losing money that he cannot afford to lose, and he is utilizing funds that family members need for their own projects and activities. He starts lying to others about where he is going, what he is doing and weaves a web of lies to his wife who discovers a shortfall of funds.
One might say that this individual is in the grips of a "compulsion," that he is "obsessed" with gambling. This appears to have become an activity over which he has no control.
An alternative view is that this individual finds gambling exciting, far more so than anything connected with work, family, or other interests. There is excitement in every phase -- thinking about gambling, going to the site where he will gamble, the gambling itself, and the thoughts afterward. There is excitement in concealing the extent of the gambling so that people at work and his family will not know what he is doing. Gambling of these proportions is an attempt to achieve a "big score", gaining a bonanza with little effort.
In reality, each time the man gambles, he makes a series of calculated choices. He is able to refrain from gambling, even for a significant period of time, if he thinks that he may be found out.
If he is finally held accountable, the gambler claims that he cannot help himself. He and some professionals to whom he turns may conclude that his gambling constititutes a disease. It is even listed as a disorder in the diagnostic manual published by the American Psychiatric Association.
However, a habit is not the same as a compulsion. Just as this man chooses to gamble, he can make choices not to gamble. If he thinks of gambling as "poison" and becomes disgusted with himself for engaging in it, he can refrain just as an alcoholic can refrain from alcohol.