It’s exciting to see Shyamalan on such confident footing once more, all these years later.
It's been six months since I last explained the theory of the idiot plot, so maybe you won't mind if I have another go. Briefly, an idiot plot depends upon one or more characters being idiots. They get trapped in a situation that they could easily get out of with common sense. But they don't, being idiots. If they did, they'd solve the problem and the movie would be over.
Idiot plots usually turn up in bad movies, but occasionally they creep into superior films like this one, causing unhappy distractions. "Wait Until Dark" is about a blind girl (Audrey Hepburn) whose husband accidentally gets possession of a doll containing heroin. After she is left alone in her apartment, three men terrorize her in an attempt to find the doll.
They stage an elaborate act in which one plays a cop, one plays an old college chum of her husband and the third plays -- but never mind. The important thing is, these three guys walk in and out of her apartment with complete freedom. The door is unlocked. First one guy comes in. Then he leaves and someone else turns up. Finally the girl realizes she's in danger.
So far, so good. We can swallow the first hour of the movie, even though it's rather unlikely, simply because we like to be entertained and want to be convinced. But after the girl wakes up to the danger she's in, why doesn't she LOCK THAT DOOR?