That kind of attitude display pains me to the bone marrow
Absolutely agree with you. I also do not like overconfident people when it comes to gambling as luck plays a very big role in this area. That's why you can never rule out that even a professional's bet may not play out. But I am very amused to see these overconfident gamblers at the moment when they lose their last money. The faces of these guys perfectly convey the resentment they feel.
Actually believing is good, but not good in some ways that must be forced when gambling. Too confident that they will win and get lots of jackpots. Even though it was just luck. Many make big bets and confidently laugh and belittle those who place small bets, even though every moment in betting such as football or horse racing can change, luck is the first. Feeling too confident will make anyone mentally down when they lose in the end.
In fact, the probability of losing has nothing to do with self-confidence. Rather, self-confidence in gambling as in everything else depends on a person's outlook on life - an optimist always thinks about only good while the pessimist is always ready for the worst case scenario. It is likely that these self-confident gamblers are optimists in life, so we observe such behavior.