Ask HN: Testing in production after deployment

I'm butting head with various people at the office and even being told that it is an industry standard to do so. I was unfortunately not given references for this point of view and all the references I could find seemed to confirmed my own point of view.

I'm interested to know if you are doing it and for what reason?

What problems do you expect you can find in production being that you are running the same code-base and likely are doing the same tests?

Why wouldn't fixing your actual development process by learning from errors found by your users/clients not work?

How the current testing methodology from a dev or pre-production environment couldn't have revealed those problems such that production testing after deployment could have?

Much appreciated!