Get into a lobby with a friend (or a random, if you must), and choose the librarian role. The checkpoint probably doesn't matter, but choose to start from the start just to be safe. Then ready up and load in to the library.

Assuming you've played the game before, you will know that there is a lever on the second floor of the library that lowers the chandelier above the maze map. Activate this lever, then go to the balcony overlooking the chandelier. From here, mount the banister with a jump, then hop over on top of the chandelier itself. From here, it is just a waiting game, literally. You will have to stick around on top of the chandelier while it slowly retracts back into the ceiling for approximately 5 mins or so.

Once the chandelier and yourself have been lifted enough, you will find that the square of ceiling above you does not have collision and so you pass through, where a secret little message has been hidden for you.

According to my partner's research, this phrase is a Dutch idiom, meaning that "a potential weak opponent may still be dangerous when forced to extremes". Put differently, "someone may make unexpected decisions when they don't have another way out". How fun.

Thanks for reading! :3