it mostly breaks CIs or docker builds if you don't hardwire the pip version, because they tend to use latest pip by default..., It's mostly not directly pip's fault, but it can get annoying.

I remember issues when they changed their caching mechanism, or when a couple of libraries I was using were importing internal stuff from pip which got changed in a new version.

Also some packages for some reason need to be installed in the correct order and it's not immediately clear until pip tweaks their installation procedure.