Just ask Ahasuerus.
Interesting how Mel Gibson treated Longinus in The Passion.
The Piercing is presented as Casca's trying to get the whole thing over with, as he is hungover and disgusted with the whole day. He was trying a "mercy kill" which backfired horribly. As Christ says to him at that moment:
"Soldier, you are content with what you are. So you will remain, until we meet again..."
He is cursed forever after that. He begins wandering the Earth, figthing in wars, always searching for the Jew he wounded.