There are some games which I lost by my own stupid mistake and then I get really frustrated, or better upset.

Don't usually get frustrated apart from when I do a really really stupid move.  Only a game at the end of the day and if someone beat because they're better than me or played a better game then I don't mind.

Sometimes I get Frustrated when I'm in a winning position and loses! That's why I occasionally get frustrated.

"it's just a game" applies only before you start and after you find yourself in a losing position. 

It's hard to get frustrated with chess though, for me.  Bad mood, sure, but frustrated, only if something else gets in the way and affects my game, like annoying kids making too much noise near where you're playing, or a bad internet connection that randomly picks games for you to lose.

u got a point there rich but you dont know some people feel

Why get frustrated it's just a game.

My biggest cause of frustration is getting disconnected in the middle of a game.