Do you know what it means to win?
Someone else had to take a loss to make your win happen.
So this is going to be a bit raw but, one day, you'll thank me for it: if you're prepared to give out losses but not prepared to receive them, then I'm afraid you just need to get over yourself. I don't want to be brusque, but there is no other way to word this.
You said it yourself, sir - nobody likes losing. You don't, I don't, nobody who posted in this thread likes losing, the people you beat in tournament or in casual matches - they also don't like losing.
And if you're willing to give them a loss, you need to be willing to take a few yourself.
Sure, the problem is that I main one of the bottom of the barrel tier characters, but hey, at least when I do beat them, I have to satisfaction of winning with a character that sucks. Like from the King himself:
I appreciate the image is tongue-in-cheek but everything I said above applies to you, my good man. Enjoy your wins, but don't forget how the other guy will feel too. Empathy matters, especially when you start going to tournaments and playing people face-to-face.
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I'm not trying to say anyone should feel bad about winning. I sure as hell don't. But I also don't forget what my win means for the guy who just made it possible.
When you understand this dynamic, losses are much easier to swallow. Especially when taken with what others have already said. At the end of the day, you have nothing of value to lose, nothing really to prove. This ain't some Yugioh shadow duel. The worst thing that can happen to you after a loss is you let it get you down and affect your enjoyment of the game. If you don't let that happen, there are so many benefits you can pull from losing a game or even a set.
Other people have touched on this, but I want to reiterate it: don't tunnel vision on winning because when you do, winning becomes empty and playing the game just becomes not fun. It should never be like that. The Smash community really is something amazing. Winning tournaments and being recognised as "good" is nice, don't get me wrong, but there is so much more that matters here, and unfortunately, a lot of people forget that these days in their quest to be PR'd or notable or some whack goal like that.
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I nearly didn't my thoughts on this topic because a lot of people don't like hearing them, but I figured you're a mature enough guy to not get offended by anything I had to say, + nobody's touched on my main point and I genuinely think it's important. I really hope that myself and the other posters here have helped you out with this, great advice has been left here and I'm glad that this thread will be useful for many more people.