A good example is the RAILS_ENV environment variable. It's a mechanism to select a running mode of rails applications. Now unlike most applications debug mode is the default. It's called "development" and the normal mode is called "production".
Because of these naming decisions developers always confuse the RAILS_ENV to be related to the deployment target. They add a "staging" running mode and they start bundling configuration secrets into the code. And invariably these secrets get leaked on github when they decide to make the repo public.
For a long time I felt something wasn't right and couldn't point the finger at it and it took conscious effort to disambiguate that. And that's just for a single variable. Mind your naming :)