The question was: Why do we accept a magical sword, and laugh at the idea of a magical toothbrush?
The answer was: Because a magical item has to have symbolic resonance between its form and its magic, so they fit together. (Plus, of course, there's the familiarity factor, but that's temporary and lesser even before then.)
So you can put on magical rings' powers like -- well, like taking off and putting on a ring. Or enchanting a sword to do with killing. We did a whole long riff on the symbolic associations of mirrors.
Then again, you need this symbolic structure to resonate with your whole stories. Which is why, I think, that I have very few magical items in my stories.