That's like stop smoking than start smoking again. It is all in your head. If you look at it like "stopping and starting again" you will never stop at all. Just get in control of yourself and even if you smoke or gamble or drink alcohol, dont overdo it. That's the key. Do not distress yourself like "oh no i said myself not to gamble ever again but i think i will" That's also a bad thing. Never say never :p

(snorting cocain or injecting heroin are all in another league by the way, you either start doing those, or never do them. once you start it is over)