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?
The game IS unfair. That's the point.
Nah I see it differently. As a veteran of Demons Souls I found very few things outright unfair in Dark Souls. Unfair as in the player is intended to lose and can only overcome by repetition where skill, luck or etc would have played no factor. It's funny when I talk to other people about the game, everyone has different things they found unfair. Some things I thought were easy others hate and vice versa.
Anyways looking back on it there were very few times I thought the game was being outright unfair instead of ball busting challenge.