We all know that a frog won't jump into boiling water and stay there. He would immediately jump out. He knows the boiling water would kill him. BUT, if you put a frog in cold water and slowly increased the temperature, the frog wouldn't realize when it was getting too hot and he would die before even knowing that he was in trouble.
I've used this analogy many times for a number of different situations. However, the one I use it most for is to illustrate how we have to keep our morals. If a guy tried to have sex with you on the first date, you'd be appalled. But if you kissed on the first date, made out on the second date, got all feely touchy on the third date, then having sex starts seeming like a good idea.
The same goes for alcohol and drugs - even lying, cheating, and stealing. Don't go there. Rationalizing your little baby steps is a slippery slope to ending up in boiling water.
Just say NO!