Asklemmy

The person who authored the cheat(s) the other person is using. Because clearly, if I lost they must be cheating. /s

For many games, I'd argue that you are to blame for your loss. Assuming the game is based purely on skill, then your ability to execute said skills is the only factor which matters. Consider something like Chess, where the game is solved and one's ability to win is really down to your ability to memorize board positions and recognize the optimal move. If you lose, it's likely because you failed to pick the optimal path.

This is mitigated, to a greater or lesser extent in games where chance plays some role. It's entirely possible to chose an optimal path, but have RNGesus decide that you get to lose today. Some games provide some ability to manage the risks created by randomness, but you often have some reliance on "luck". Obviously, the more luck dependent a game is, the less control you have over winning/losing.

And then there is the issue of other players who can affect the outcome. If you play a game where there are more than two players, the other players may be able to change the course of the game enough that, no matter how well optimized your choices, you cannot win. This leads to the classic "kingmaker" problem in board games. It may be that someone who is themselves unable to win is in a position to directly effect the outcome of the game in such a way as to make another player win or lose. So, maybe you played a very good game, but the kingmaker decides that you lose.

Ultimately, the answer to the original question is, "it depends". And there are a lot of factors one must look at to come to an answer. And that answer is unlikely to be whole one thing or the other.