You learn skewers by practicing them a thousand times. Not by having a GM show you your mistake once over the next hour. Chess, at 1500 Elo, is decided by one mistake like that.
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There's also the chance that the GM performs a checkmate in 7 vs you. This is too far ahead for a 1500 Elo player to see, but something easily within a GM's grasp in the midgame. In this case, you learn nothing (you shouldn't be looking for checkmate in 7 or that depth as a 1500 Elo player)
This is why playing vs Stockfish (superhuman AI) is useless. It doesn't teach you how to think like a human or how to get better at chess as a human... all of Stockfish's moves are so deep that they're AI only.
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Its different if the GM is explicitly performing a "teaching game". (Ex: Hey, you can be pinned with this move, lets go back 2 moves so you can try to avoid it). But if the GM is there to troll you with shitty strategy because they're way stronger than you (ie: most online smurfs who are +200 or so Elo above you), then you learn nothing and simply serve as the opponent's entertainment for the night.
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Same thing with fighting games: go into training mode, and perform your combos another hundred times. You learn nothing from the opponent comboing you though.
Same thing with RTS games: go into training mode, and practice your build orders another hundred times. You learn nothing by the stronger opponent executing their build order perfectly.
Same thing with League of Legends. You learn nothing when the stronger opponent team combos / ganks you out of position. You need to practice your ganks (which are likely a different character, so you'd need a different set of spells used at different timing).
Etc. etc. Training / getting better at a game is very different from actually _playing_ the actual game.
Unless the opponent is purposefully throwing a "teaching game" and/or giving an appropriate handicap of some kind, this is absolutely not the case.
In Chess, games at the 1500 Elo level are won/lost due to a knight fork, a bishop pin, a skewer, and other such traps. GMs literally will give you _zero_ opportunities to find such mistakes from them, because they play nearly perfectly.
Finding such mistakes (in yourself, and your opponent) requires an opponent who makes such mistakes at a roughly the same level as you. GMs who can see maybe 2 or 3 moves ahead of you will prevent such mistakes from even occurring, giving you no chance to learn.
A "show match" vs a stronger player is to be honored, but its not a lesson learned. Its not a teaching game.
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Sure, GMs make mistakes. But the mistakes they make are invisible to 1500 Elo players. There's no hope to ever see it, and no one expecting to learn to play the game studies GM-level chess.
1500 Elo players will improve far faster with skewer puzzles, fork puzzles, outposts, etc. etc.