Well, it is for various reasons, but most obvious is that in one point of the game we did have advantage, went too much happy about it and blew our advantage and didn't even felt we blew it. So, problem is in our mental state and not in our gameplay that we have this feeling that we should have won the game but we didn't.
In other hand, there are times when we feel we did something good that is actually GOOD in game but the opponent is just too strong and it didn't affect him the way we did think it was.
Think about it as this: You make strongest blow you ever imagine, you think: «Man, I did punch this time so hard I never knew I have so much power» but on other side you did punch a stone that didn't feel it. You think you did something GREAT and you did, but it just didn't impact him as you did think it did and well… he won the game and you have your question mark floating over your head. He was just too strong and you were evaluating yourself and your game, not his nor his skill.
Problem with this mental state is that it can be devestating to newer players who think they are doing good but they just can't break the ice and they just support the effect «I suck» that they carved into their head.
I was in 1001 situation where I did feel I did so much better then my opponent just to see him make more army and roll me over. And that's it. He just made more and killed me.
Problem is that I FELT I harassed him so much he couldn't have so much army and that I did MACRO so much better then him… but in reality I didn't. Problem with people is that they sometimes overevaluate themself and think they are good and doing good and sometimes they do the oposite — they understimate themself and don't do 50% of quality gaming they could because of mental blockade. Also, it's very importan that you know that everything that IS and is an outcome is an direct product of SOMETHING, and by that I mean he didn't WIN just because he did, he did win because he was BETTER. It's very hard to pinpoint segment of LUCK somewhere, sure, your mouse can slip and you can miss storm or two (by the way, we can treat this as less of practice and skill because maybe this wouldn't happen to you if you did practice more?) in the end just don't balme something that you don't have control over for your loss. It just doubles the «Why did he won I played better» effect.
The best path is to clear mind of those toughts (toughts in chaos :D ) and just play the game. Put your CJ face and just take it and give it, don't think who is better or did you done good… just play and do your best. In end, it dosen't matter if you «feel you did good» — only thing it matters (for competative game, let's not make assumption that I don't like fun in this game or that im «only wants to win robot» — far from that, but I'm writeing from perspective of a player who has a goal of improveing and wining most of his games.) — WIN.
This subject is very complicated and I am 100% I will write about it more with my experiences thrown at table (people just love to read experiences and personalize themself with them) so expect more from me on this issue. Yeah, it's an issue because it is such annyoance that makes you stop improveing and make your Starcraft experience less fun and enjoyable.
Take care,
— ReiKo.cry