Call of Cthulhu
49 Achievements
12-15h
Ex Oblivione
Fail a skill test
72.2%
How to unlock the Ex Oblivione achievement in Call of Cthulhu - Definitive Guide
Your first opportunity to get this is at the beginning of chapter 2. Put no points into medicine during chapter 1 and you will most likely fail the medicine check on the dead whale carcass to the left of the starting point. You know you failed the Medicine check on the whale if you get the lines: "The blood is beginning to coagulate. Only a specialist would know what killed it."
If you don't get the lines above, no worries, you'll fail dozens of checks during the course of the game.
Edit: Nothing about the specialist. And, no, I didn't put anything into medicine.
Edit 2: I got it, I finally got it! It popped while I was talking to Fitzroy.
First, look at the newspaper clippings on the desk, turn around and view the painting on the settee, you should then fail that and unlock this achievement.
Very Easy, go to 5:20 in Playthrough 1 video to see this.
Hope this helps!
Playthrough 1
Playthrough 2
You unable to unlock it?
Have you tried just hard resetting the console?
There are many skill checks in the game that you could possibly get this with. Some are trivial, such as the dead whale right at the beginning of Chapter 2, while otherwise will block progress toward other achievements. If you don't put any skill points into Medicine during Chapter 1, you'll get this with the whale next to the pier.
I got this trophy at the end of the first chapter when you need to interact with the painting in your office. You need to hold to do so, and a simple tap on would “fail” the challenge, unlocking the trophy.
If it doesn’t work for you, you can get this very early on Chapter 2, go interact with the dead whale and as you won’t have enough skills to find out the cause of its death, you’ll earn the trophy.