~ It all depends on the character of the person. And also from his mental abilities. If a person is good at mathematics and knows something about probability theory, then he will certainly understand that the probability of winning in the long run is always much less than the probability of losing. But still, some people believe in their luck, in their good karma and play risky.
You know, that's not the worst thing that can happen here. I mean believing in "their luck, their good karma" and stuff. I personally wouldn't recommend this kind of thinking for gamblers, but that's not the worst that can happen to them. The most terrible thing is to think that you've figured it out, you know exactly how to win, all calculations done, you just need a larger bankroll for that.
And of course he loses as a result. But sometimes it's not a disaster, but just a life experience and a great lesson for the future. 
As I said earlier, losing is not guaranteed, same as winning. You can invent a craziest strategy of betting one can imagine, and be winning with it for a long time. It will be an outlier, yes, but with over a billion gamblers in the world almost everything is possible in one particular case.