The trident only works for Atlantean royalty, shocking anyone else who tries to use its powers. This also makes Arthur resistant to its magic. Orm uses the trident's magic, which can only be wielded by royalty, to imprison the Justice League. After Arthur wakes up, he gains control of it and escapes. Might be justified in that Arthur is a illegitimate, and Orm's egotistical enough to believe that meant he couldn't use the trident's magic. Orm calls the trident to his hand at one point. Wonder Woman wasn't strong enough to stop it from reaching him. Orm does this with the trident to slow his fall during the final battle. Arthur learns how to use his trident rather quickly.