> why if you have this confidence that your first three questions contain 90% of the signal, that you spend the rest of the interview doing anything vaguely related to that?

When interviewing people maybe one in six answer questions correctly and in-depth, one in six do very poorly, and the other two thirds do so-so. The two thirds are all kind of interchangeable - they can answer most simple questions in a basic manner, missing a few here and there, but can't go into much depth on things.

I would say it is kind of a strict culling thing. The purpose is to find the one in six who can answer the questions well. There's not much reason to change it up much with the twelfth interview who is doing so-so, because if I interviewed twelve people I probably just talked to two people who are a standard deviation above the person doing so-so. So I want to talk more with them, not the one who doesn't know anything in-depth.

On the interviews where they're really stumbling, sometimes I have felt like standing up after only a few questions and going back to my work. Initially I am never focused on one particularly area, I am jumping around in case the last question was in some area they have a gap in, and perhaps they have a strength in some other area. I use their resume, and ask them directly about the areas of strength, to guide this. If they tell me they are strong in an area I will certainly ask them some questions in that area. If I know early I will say no, but keep asking questions any how, I suppose I stay the minimum amount of time I can without seeming rude.

The one in six who do well, those are the ones that I "pivot to something like trying to evaluate their conscientiousness or openness to learning or emotional intelligence or ownership of their previous projects and mistakes and such". Or more broadly, get a sense of their personality, how they will fit on the team, what their expectations are etc. I suppose it is almost the pattern as the technical questions - one in six will have some obvious personality quirk (they really don't listen to what we're saying at all, or they are very obnoxious, or they seem uptight beyond being nervous at an interview - or they take a pen out and start writing on different objects in the office, and the the boss comes by later and asks who wrote over everything and you say the interview subject, and the boss asks why you didn't stop them from writing on desks, walls, machines etc. with a pen - yes, this happened), two-thirds seem normal, and one in six is very friendly and/or seems like a real go-getter with a lot of accomplishments under their belt. I'm pretty lenient at this stage, although others are less so (also, I wouldn't mind having a teammate who would gripe about features and projects they thought were BS, but maybe my team lead or manager would mind - so a pass by me for this type might be a block by them).

So in short, I don't even try to fathom their "emotional intelligence" if they're stumbling on easy questions.

Insofar as teachability, we're usually hiring for a role. They're also being interviewed by multiple people - my technical assessments of the one in six who are good usually matches my coworkers. I tend to be more lenient on personality, emotional intelligence etc., they will say no to people I say yes to. So even if I was more lax, they are not, and they won't get in. Usually there is not much leeway, we are hiring for set roles. The main leeway people get is if they know someone in the group already. If their friend works in our IT group, and they know the subject but not in-depth, we often OK them on the basis of the recommendation that this person is the type that will get up to speed.