I tend to agree, that such question is indeed a great way to start a productive conversation, especially with addicted gamblers, but I can't agree on the second part, that you have to bet high to be able to win big because there are dozens of lotteries and other opportunities were for literally 1$ one can win millions of $$$. Let's take Euromillions or any other national lottery as an example.
Of course, these can be used as an excuse by gamblers, when they are on the losing strike and already lost a lot of money, but still, this is only an excuse. This is true that it is very possible that one will win big if bet high enough, when betting on sport or horses, but in real life, the biggest wins are gained for the price of mentioned above lottery ticket, which costs usually 1USD.
This is true because addiction is very sneaky. I keep repeating this same (already gambling almost 20 years) because I had never problems related to my gambling (money, personal life), but to be honest, only a close friend, family or specialist, would be able to notice or diagnose addiction correctly. Many times one can just afford to gamble and lose significant amounts of money, but this doesn't mean that he is not addicted. I think, these are the toughest and most difficult cases, which are the hardest and sometimes almost impossible to get help.