If somebody doesn't understand how to play your game, it's your fault.
If somebody can't extract basic principles from the rules, it's really your fault.
As long as they can read, and are trying to understand, they are absolved of any blame.
You can make all sorts of excuses, but that's all they are - excuses. Some are good excuses ("this game is pretty complex", "space/financial/time constraints limit the size of the rulebook"), some are really bad ones. ("This game contains radical ideas that are beyond the comprehension of the unwashed masses.") They don't absolve you of the responsibility.
The bottom line is that it is your job to make them understand.
And yes, it's bloody hard. It's probably impossible.
But you have to try as best you can.
And if your efforts leave a significant fraction of the audience scratching their heads and getting it wrong, then your product is defective. You can do a lot to mitigate the problems after the fact, but it is less than ideal.
Just don't insult people for not understanding. Don't tell people that the game you're selling is not designed for them. If it's not for them, don't sell it to them. Don't say they don't understand because there's something wrong with them.
(And yes, I freely admit that the rules of Shadowfist are not as clear as they should be. I have excuses, but it's still my fault. I can duck any blame on Angband's documentation for now, but only for now.)