on Jane Friedman site:

Writing a tightly plotted and twisty thriller, mystery or suspense novel can feel like assembling a puzzle where none of the pieces seem to fit. This pain point often makes itself known when we sit down to write the climactic scene, when everything must come together and be explained, and we realize that some aspect of our story setup is fundamentally broken. The protagonist can’t have the “A-ha!” moment we want them to, because the logic doesn’t work, which means we can’t write forward or through. And because we’re already so deep—months and years of writing, planning, and revising—this block takes on epic proportions and can feel like an insurmountable wall.

Obviously, by the way I talk about this, I’ve been there, and I’m here to tell you there’s a path through.

The solution is a deep dive into the villain’s logic: understanding the motivations, logical actions, and misinterpreted “on screen” clues of the villain.

Before we go further into this, let’s take some time to define what a villain is, and isn’t.