I was in a meeting with a colleague about a PR for some python code. One of the things I noticed was that he had an unused module that contained an import of a non-existent class from another module. I know he uses Pycharm, so I mentioned to him that this kind of thing should be hard to miss, because the linter in Pycharm should have marked it, and the folder it's in, as red.

He tells me, and I quote, "Oh, all the files are red."