Most of the infamous NES games aren't even actually hard, they just try to prevent you from practicing with bullshit checkpoints and limited continues.
Like the final bosses of Ninja Gaiden aren't difficult, but good luck figuring out the fight when every time you die you're kicked back to the start of the world.
It's no wonder that these games get utterly raped by save states that let you practice one part as much as you want without having to go through what you already beat everytime.