"It's volatile, but not faulty. If you mess with something big and mess it up, if it fails it will fail spectacularly. If it's a little thing the backlash is minor, but try to avoid it then, too. I know some people that can't leave their Avalon because they can't fit in to normal society 'cause of magic tweaking them. Things that go wrong you will have trouble fixing. So don't get 'em wrong and if you're not completely sure about what you're doing, don't do it."