Wizards draw in energy

Q: As far as how the thorn manacles work:
A: Essentially what it does is when a wizard’s drawing the magic in, the thorn manacles divert it to somewhere else. Wizards have to give a little bit of energy from inside themselves, but mostly that’s to pull it in from the outside.  And the thorn manacles take that and go, “Nope, ok, we’re shunting it out into the Nevernever and you don’t get to use it.”
The pain is just a result of the energy that is going by and going elsewhere, it’s inefficiency of transfer, if you want to put it in engineering terms. That’s really nerdy, so I won’t do that.

2015 Stokie signing (http://www.jimbutcheronline.com/bb/index.php/topic,46159.msg2184778.html#msg2184778)