Okay, so let me present you with my view of the game. It's going to be very different from yours, and it's fine if you disagree. In fact, in the first few years I played, I would have had a hard time agreeing as well. But I'd appreciate if you hear me out.
1) On average, ranked players play at a skill level consistent with their rating. In other words, even if they have the skills to play better but don't, their rating should reflect this--on average.
2) For each individual game, there can be some variance in individual performance. Sometimes matchups are lopsided, and sometimes mistakes are made. Sometimes you're on the team that benefits, and sometimes you're not.
3) Trends are more useful than individual games. "Did I do better in the last game than the previous one?" is not always a useful question, so I'd rather ask "Did I do better in the last 10 games than the previous 10?" This follows from 1) and 2).
4) Morale affects the game, and my actions can affect morale. It's really easy and tempting to call out gameplay mistakes, but I think that only serves to hurt morale. If I still wanted to win the game, making my team feel bad hurts my chances. If I prefer to surrender, there are better ways to convince people.
So yeah, the reason I wrote this is because I've definitely had my share of upsetting losses, but I found that shifting my mindset helped me deal with it better.