When I was a kid I admit this was rather common with me, even with games I loved I often felt like I simply lacked the ability to actually see some of them through to completion. As I got older this changed significantly and I don't feel this way about most games, especially when I learn I don't need to always restrict myself to playing something a specific way (like after four hours of trying I just accepted Melania in Elden Ring was too much for me to handle doing solo so I began to rely on the Mimic summon to finally feel like I had a fair chance, though I guess it's worth noting that I did avoid summons for the actual final boss).
However there is one example of a game where I feel like I legitimately lack the skill to beat as an adult. That game is Crypt of the Necrodancer, and I specifically am referring to getting the game's true ending when playing as the character Aria. This game basically requires playing through it three times as three separate characters in order to see the full story, but the final character, Aria, is by far the hardest. Unlike Cadence and Melody, who only suffer a combo multiplier loss when accidentally missing a beat (one of the game's main gimmicks is all actions are tied to keeping to the beat of the music playing, the game is described as a "roguelike dungeon crawler and rhythm game jammed into one," you can even play it with a DDR dance mat if you want), Aria outright takes damage when missing a beat, and what makes this harder is she literally only has one health AND you HAVE to use the game's weakest weapon, the dagger, to boot. You're allowed only one screw up thanks to Aria having a revive potion on her, but once that potion's gone you have to pray RNG will give you other damage mitigating items like glass armor or a freeze charm. I tried for multiple days to get through just ONE zone as Aria, and after so many losses I just came to the conclusion that, simply put, I lack the skill necessary to beat the game as Aria and I just looked up her story cutscenes online so that way I could see the true ending and be ready for when Cadence of Hyrule (an officially sanctioned crossover between COTND and Nintendo's The Legend of Zelda) came out.
I still enjoyed COTND, more so when playing as the primary character Cadence, enough so that I bought Cadence of Hyrule when it came out and I'm looking forward to the upcoming sequel which looks to also be taking inspiration from Rhythm Heaven, but I've just accepted I simply lack the skill to beat the game when playing with a character whose whole gimmick is "you literally can't miss a beat or take damage twice or else you die, oh and you can only use the game's weakest weapon."
So hey now that I talked about my own personal example of a game I just can't beat, do you have an example?