The Council

Using many skills in the game cost effort points, denoted by the diamonds in the bottom left of the screen.

A great place to unlock this is Episode 1, Quest 3, when you have the objective to "go to the red salon on the first floor". On the first floor is a servant you can talk to and ask about the mansion, the guests, etc. One of the options is to ask the servant to get you items – you can ask for one of each consumable, one amber and one manuscript. They are all helpful and most of the options you have to convince him to help you will cost effort points. Just remember that servants are vulnerable to manipulation.

This is also fairly easily unlocked during the Medusa puzzle (see Fearless) in Episode 1, Quest 4, if you examine each statue and use effort points to get hints on what to do. There's also a book on the wall you can use a few effort points to translate.

Note that if you successfully exploit vulnerabilities in the game, you will gain back at least one effort point after you do so. This trophy will not unlock if the effort points are all expended on an ability that exploits a vulnerability, because as far as the game is concerned, you didn't really get down to zero points.