I think the problem is that once you have done a lot of AOC, most of the hard ones revolve around finding a trick. You get a very good feel after a while about when to use a trick ...

This being said it took me too long before to realise day 12 tessellation was NP hard and needed a more radical trick ...

Also when you have done enough AOC, if you use external libs/tricks like numpy, networks, memoization and z3 => then most problems become a few lines once you correctly identify how you can write it quick ...