One of the things that seems to help DS5 is me not giving in to him "quitting" something...
In fact, just yesterday, we were playing hangman while DD3 was in ballet class, and during the last game, he kept getting so frustrated about not guessing the right letter each time. He kept saying "I can't do this. I can't guess the right letter. I don't know what it is", etc... Along with reminding him that the game isn't over until he either guesses it correctly or he is hanged, and letting him know that it's ok NOT to get it every single time and that some will be harder than others, I made him take time outs. These aren't actual real time outs, but they are moments, even if just a couple of seconds, for him to regroup his thoughts and with hangman specifically, focus on the letters he didn't guess yet versus the blanks that are remaining or how many body parts are now drawn. That may not make much sense, but perfectionists can get stuck on a negative aspect of something and almost hyperfocus on it. And while they may be perfectly capable of thinking outside the box or coming up with more than one solution to a problem in "normal" situations, being anxious about that one negative aspect and not being able to "escape" that feeling can cause real problems.
I refuse to allow either of my children to quit an activity just because they had a bad day - something my mom allowed me to do. And even to this day, I have to fully force myself not to just quit something due to a bad day or because I think it might be hard (a job, a team, school, a class, etc). DS plays baseball, and every season he plays, he knows he's not allowed to quit midseason. I also think that him being involved in something that he's not really "perfect" in helps... he's no where near the best kid on the team, which motivates him to try to get better, but it also gives him an idea that there will just be some people better at somethings than he is. For us, baseball (and Monster Trucks & NASCAR - his two other "loves") is perfect because even the big shots lose, or strike out, or don't get to play one day, etc...
