You have a good point, but it may not be as simple as just to expect less, some conditions must make that possible. Most people have positioned their minds too high in gambling and the profits associated with it. This is why they commit big amounts of money to it. Now tell me, can the person who bet/risk big expect less? That's the issue, because such a gambler did not gamble with the amount of money he can afford to lose, and no matter how he wanted to fight his psychology to stay calm and expect less, the emotion attached to that big amount will not let him.
Such high expectations are always fueled by stories about players who managed to win very large sums in the casino. And then a crowd of other players runs to this casino and starts playing the game that brought fortune to the user from the beautiful story. And when you have already heard about winnings of x3000-x10000, then x3 of your bet will not suit you. You will want more, because you think that if someone succeeded, then why shouldn't you succeed. But the fact is that only a few succeed, and everyone else loses. And there is no way to predict in advance that you will become such an once-in-a-lifetime case.