It's pretty daunting when you're invested into something, spent a plenty hours only to realize that you're not in those 5% who's going to complete this challenge.
IMO AoC should strife to be completable by 80% of programmers (number is out of thin air, but you got the idea).
I for one want that 5% to have interesting challenges, even if I can't be a part of that 5%. Unique achievements should be meaningful and celebrated, not removed for fear of upsetting the majority who cannot achieve them.
While I agree with the sentiment of creating accessible content I think if you make the problems so easy 80% can solve them, what fraction will have fun doing so? Wouldn't say 50% find them trivial and boring/unsatisfying?
I think AoC goes for slowly growing difficulty which helps keep more skilled people engaged.
For what it's worth, I'm not a (professionnal) programmer, and I can usually solve 80% of the AoC problems intuitively. That's OK for me.
For the other 20% where I don't even know where to start, I look up a solution on reddit, try to understand it and re-implement it myself, and learn something new. The 2020 day 13 problem mentioned by GP was indeed one of those for me last year.
Honestly, I didn't even understand how the CRT applied even after knowing it was required. This visualization[1] is what eventually helped me solve it.
IMO AoC should strife to be completable by 80% of programmers (number is out of thin air, but you got the idea).
Project Euler is a different beast.
Of course that's just my opinion.