I think this article – The Most Dangerous Word In Software Development – hits the nail on the head.
“Just” implies that all of the thinking behind a feature or system has been done. Even worse, it implies that all of the decisions that will have to be made in the course of development have already been discovered—and that’s never the case.
Every time somebody asks for “just” this little thing or that little thing, I ask them to “just describe it”, or “just answer a few questions”, or “just pay for it”. Somehow, it never turns up as easy and simple in the opposite direction.