Completing the Contradiction quest in Crimson Desert is a little tricky. Unlike any previous investigations you may have done, such as Close Threat where you have to give evidence to Shakatu, this one is just a series of two-choice answers.

There are no items involved at all, so which one you pick simply depends on how well you listened to the testimonies of the various suspects during the investigation. I don't know about you, but I'm not always the most attentive with NPC dialogue, so here's what to answer in order to unmask the correct culprit who stole the forbidden book.

How to complete Contradiction in Crimson Desert

When you speak to the Institute Steward, he'll roll through each of the suspects one by one, to which you have to choose one of two responses. Here's everything you need to say in order:

1. "Heard there was a meeting with a noble from out town that day."
2. "They were at the lab with Tarho all day, and reckon the guard's the one acting suspicious."
3. "While working on their research with Grunil, they stopped by the library and got scolded by the librarian.
4. "It seems the library has records of everyone's visits, except Raphael's."
5. "They insist they couldn't have stolen it - since they didn't know about the forbidden books or the ancient language."

After this, he'll send you to catch Javier down by the library. A cutscene will play in which you knock him down, then it's simply a case of tying him up and delivering him like a bounty to the authorities in the courtyard nearby.

You'll get the reward, and that'll be The Weight of Knowledge quest completed.