At work, one of our customers is known to be "unique"/"challenging". The customers normally talk to a person (let's call this the middle person) who used to work in the customers' field and translates their requests for software developers. The customer had gone through >3 e-mail rounds with the middle person and I as we tried to build an item to her liking.

After the last e-mail complaint, I printed out all of the e-mails related to the topic, all of the example cases she pointed at, and tried to figure out what state of mind would make her so frustrated and have so much trouble getting us to do what she wants as opposed to simply taking each e-mail at face value. I made one more tweak to the product, e-mailed the middle person, and held my breath.

This happened about 2 weeks ago.

My company hasn't received any more e-mails about the product so it seems to be a great success.

I post this anecdote here because the idea of approaching the problem like that was almost certainly taken from HPMoR. Quote is below:

Harry kept his expression blank, and realized one second too late that it might as well have been a signed confession. Professor Quirrell didn't care what your expression looked like, he cared which states of mind made it likely.

Caution: This probably only works if the person you're modeling is sane.