Personally, a a bettor, I find it very stressful when watching the game you are betting especially if it will end up a losing bet.
If we have the same experience, how do you cope up with that problem, after all, gambling should be fun but why we have this kind of feeling that we feel disappointed when our bet loses?
Simple answer: it is because money is involved.
Take away the monetary aspect of gambling, then everything would be bleak and boring. The potential of a person winning big is what makes gambling so attractive to users. Given that a monetary aspect is involved, this also contributes to the adrenaline feeling whenever people bet and risk their money. After all, gambling is mostly about luck- watching your odds win/lose can make you feel both excited and anxious at the same time in which some people crave for such feeling.
In conclusion, when money is involved, then people would feel anxious about their bets. If they win the bet, then they would feel ecstatic; but if they lose, then the feeling of regret and revenge are mostly the initial reaction to people.