They are rarely unfair, it's usually a question of changing your approach and there are often several different ways to tackle a situation.
Oh come on. One of the very first encounters has rats with poison bites hiding just around a corner and right next to a death-drop ledge. Or how about skeleton wheels, which if they hit you are basically instant death? The poison dart enemies who attack FROM BEYOND THE PLAYER'S VISION? The endlessly respawning mosquitoes in the swamp?