When did losing become precious?

I was playing Super Smash Bro.s Brawl with my girlfriend tonight and she kept getting upset that I was setting the computer opponents difficulties up to high. I'm pretty good at Smash Bro.s, I've been playing the series since the original, so Renae never wants to play against me head to head because try as I might she gets upset. If I screw around and don't take the game seriously she gets angry and if I take it series I mop the floor with her avatar and she gets even more upset. Her complaints were loudest when the cpu controlled fighters beat us both before the end of the match and we had to watch the end of the fight play out with no input of our own. I realize now that the reason why she got upset with me then was that my meddling was causing her to not have any fun. I set the difficulty up so high in the first place because I like a challenge, and just fighting her meant there wasn't much of any. So I called her a sore loser and wondered why she was so upset. Maybe one of the reasons why Rock Band and Guitar Hero are so successful is that players can set their own difficulty challenge without interfering with the other players. Maybe I'm just so used to being beaten by a smarter, faster computer that I don't care about failure anymore.