Sooner or later, they will addicted to gambling. Once that is happen, they will ruin everything they have and even their life.
Each gambling addicted is different. Being gambling addicted isnt something uncurbable and does not mean that everyone will ruin their lives with 100% probability. I think everyone who has tried gambling at least several times are already addicted, because they return to gambling anyway. We have different forms of addiction, someone return and gamble daily, someone on special occasions, someone gamble once each month. But that does not mean we all are moving towards ruining lives.
I agree with you that addiction is not inevitable for a gambler. Some people may be afraid that if they start gambling, they will continue to lose money. I think they are confused about their future and their negative perception of gambling is very wrong. A gambler does not lose every time, they have a strong desire to win, which means they will not win a lot. Luck is considered a key factor in their winning and losing in gambling. The more experienced you are in gambling, the more you will tend to be lucky. Luck is often blamed for gambling addiction, just as people always blame themselves for their bad times.