Once upon a time (and isn't that how all good stories start?) I was managing a software team and we were working on several initiatives. Projects were assigned based on who was available, their skillsets, and their development goals. This resulted in two developers, let's call them Mary and Melissa, being assigned to the same project.
Mary and Melissa had been working together for a few weeks when I started hearing complaints in my one-on-ones with each of them about the other. Mary was complaining that Melissa was taking too long to do her part, and spending time on unit tests that did not make sense because things were in flux with the project. Meanwhile, Melissa was complaining that Mary wrote sloppy code and did not write enough tests (she even showed me comments in the code like "hack:...." and "to do: someone should add more error handling here"). Each of them had valid points and feedback for the other.