Medieval Islamic scholars distinguished two kinds of ignorance: 'jahl basīt' — simple ignorance, not knowing that you don't know — and 'jahl murakkab,' compound ignorance, the condition of believing you understand something you've fundamentally misread. Ibn Khaldūn, the 14th-century historian and social theorist, built his entire theory of civilizational collapse around compound ignorance: ruling classes who had constructed such internally coherent explanations for their world that they couldn't register incoming evidence that contradicted it. Their models worked — right up until they catastrophically didn't. This is the engine your thriller might be missing. Most plots give the protagonist a knowledge gap to close. The more unsettling structure is a protagonist whose competence is the problem — someone who is excellent at reading a situation that has quietly ceased to be the situation. The horror isn't that they're stumbling in the dark. It's that they're moving with total confidence through a room that was rearranged while they slept.

What does your protagonist's competence prevent them from seeing — and how early in the story could you plant that blindspot without the reader noticing?

Drawing from Islamic Philosophy / Historiography — Ibn Khaldūn (Muqaddimah, 1377 CE)