What is the need of getting upset when we already know that gambling is a game of both losses and wins, and before we set out to gamble, we should already have it at the back of our mind that it a game of chances and we should only use the amount of money that we can afford to lose and be OK with, this is what we should always look out for in games and not the over expectations of winning.
If you have free time, ask your friends to play any card game or football game that doesn't involve money, something just for fun. During the game, observe how each of your friends reacts to the game's outcome, and you'll see that those who are losing will become irritated, nervous, and may even be insulting each other. They won't accept the results, accusing their opponent of cheating.
By the end of the game, your friends will be even more irritated, and when the game is over, you'll see that the atmosphere won't be good. Those people who were happy and chatting before the game won't be the same at the end. Most of them will be angry and won't accept defeat so easily.
What I mean by this is that nobody likes to lose, even in games that don't involve money. People still don't want to lose; for them, victory puts them on top, above the loser. So, in gambling, people who can't handle losses in games that don't involve money become even worse when they lose in games that do involve money.