There is no straight line between hard and unfair, friend. To make something 'harder' there would have to be a disadvantage to the player, therefore it is always unfair. Of course it's perceptive of how one would see anything being unfair. But I can argue that in any game other than Pokemon that receiving more damage in hard mode is unfair. An item worth more than it should: unfair. A boss with an even bigger health: unfair. You can't make an omelet without cracking a few eggs.