When does a clever exploit feel earned instead of the author cheating?
The best moments in this genre for me are when the MC breaks a fight or a system with some loophole nobody else saw. But the exact same trick can land completely differently depending on the setup.
Earned version: the rule was established chapters ago, using it costs something real, and other characters could have done it but just did not think of it. You get that 'oh, of course' feeling and immediately want to reread the earlier chapter.
Cheating version: the loophole shows up in the same chapter it gets used, or the system suddenly has a convenient blind spot it never had before. Feels less like the MC outsmarted the world and more like the author reached in and flipped the board.
For me the dividing line is usually whether the exploit creates new problems. A system that gets abused should push back somehow. Patches, attention from the wrong people, side effects. If the exploit is free and permanent, it usually reads as cheating even when it was foreshadowed.
What is an exploit moment that completely earned it for you? And one that felt like the author cheating?