Thanks to God, the alcohol is not a problem for me. I drink only beer, and not often, and avoid abusing it. I feel blessed for it (my father was an alcoholic, died, very sad stuff).
But pot can be a serious problem for me. It leads me to weight gain, and then I get depressed. I lose the will to study and to try hard. I become a master on procrastination. And there are some spiritual issues, too, I guess.
So I think "if I smoked just once a week wouldn't be a problem". Probably right, but it's really hard to say to myself "not today" when I have it in my drawer.
Luckly, it's rare to have pot in my drawer. I don't know any dealers, so I depend on little gifts from my few friends. I often get frustrated for not having pot. It's tricky: when I don't have pot (almost always) I feel frustrated, and when I have some, I smoke until it's over, in some kind of compulsion.