"First, he pointed that giant metal rod at me and out came a glass vial, it exploded next to me! Next thing you know, out comes a friggin’ bear! Then, as if that wasn’t bad enough, he sticks it in the ground. It expands and he walks into it to get a snack!" - Xzud, Experimental Arms Dealer.
Believable magic, like ordinary physicis, operates according to some invariable laws that always result in some kind of cost or "bounce back". The grater the magic, the more it should cost the character physically, emotionally, and spiritually.