Well, I don't play much multiplayer, and when I do it is with someone I truly like, and take pleasure even if he is winning.
Single player I do not have the patience to try a scenario 10 times just to win. I will mod, use trainer, use Cheat Engine, whatever, to get through that scenario. Most of these games I avoid, as they are not historical based and artificially made difficult.
I am actually happy to lose to a decent AI, but have my limits. I will mod and cheat and experiment if it furthers my enjoyment of the game. There is enough stress in life, so no way am I bringing that into the gaming world. But yes, maybe people who are super-competitive and really take this stuff seriously, it could be frustrating. And there is nothing wrong with being competitive.
Take some of the Ageod games. They are hard enough even to understand how to play sometimes. So I take great pleasure in modding myself an advantage and seeing how things turn out. This is something a real historical-minded player would abhor. On the other hand, it is often not about winning, but how enjoyable the game is to play. If I'm playing Command Modern Naval Air Operations, I always play in "editor" mode and experiment. Winning the scenario is the last thing on my mind.
However, I admit to get frustrated with some consistently bad, or seemingly "unfair" internal dice rolls. In those instances, I am tempted to cheat through it when possible.