One of the things that I worry about is a behavior which I shall call "building alien artifacts". This is where an external team (it may be external consultant, or in-house people, or even just senior people within the same department) help build a project in a manner that the incumbent team cannot fathom, maintain or update safely. Essentially an alien has dropped this highly useful, well built device into your lap, and if you press the wrong button, or combination of buttons, it's likely to explode or at the very least give you a nasty shock. To reinforce what I'm talking about here, the aliens have built a good system, not some piece of crap that can't be maintained, but the how and why is beyond the capabilities of the team who must take it over.