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And within myself, I am still wondering, what could possibly lead a person back to gambling after successfully quitting initially? Know well the reason for initially quitting was addiction, does it make sense to go back to gambling and become even more addicted?
Well, the main point of the parable you took from the Bible is that it is not enough to simply get rid of evil or bad habits. You have to replace them with something good. If you dont fill the void, something worse will eventually take its place.
It is possible that this is what happened in the case of the guy you mentioned. After taking the step of eliminating his gambling addiction, he failed to take the next step of filling the void with something good that would give him pleasure. The thrill, the risk, the instant gratifcation was part of his routines and his psychology. He did not replace with a new passion, a new purpose, or even just a new hobby that gave him the same thrills, so when the gambling "demon" returned, it did not find an empty house; it found a ready welcome.