Specially the ones where you have to find stuff.
I usually attempt and manage to get them without looking up any info, but other times I miss something and I don't want to go thru the tedious process of re-combing whole sections of the levels, or even starting over, just to find some stupid note that I overlooked. Yet, I want the achievement, so I end up looking a guide and I feel like I haven't truly earned the achievent.
Yes, I know that playing a videogame shouldn't become a task and that I simply should play it the way I enjoy it the most, but I want too see what others think.
With the exception that if it's a multiplayer game that your enjoyment is not to the detriment of other players.
I ran Game servers 20 years ago and people used to get upset when they were banned for cheating. They 'have the right to play the game the way they like' was a legitimate argument directed at me.