One of He-Man's running gags is Orko poor magical skills, in that nearly every time Orko attempts to use magic, it backfires. He also has a seemingly magically-imbued hat that can contain many more items than the hat's outside appearance and size would suggest.
It's never made clear why Orko is so inept, from Orko supposedly losing an amulet that allowed him to properly use his magic, to it being suggested in an episode that Trolla's natural laws are opposite of Eternia's.
See all ten not-so-wonderful wizards at Geekosystem. Link