Mysteries and thrillers have two kinds of revelations: who the villain is and the motive of the villain. In my WIP, I am trying to present a few possibilities about who the villain is, but I have no doubt that maybe half of the readers could guess who it is, even if it's just a pure guess without any rationale. I also reveal why this villain is doing the horrible things to my MC. I will be very surprised if the reader could also guess the motive I have written for the villain.

So which has greater impact? The who or the why? Or are they both equally important?