The GM's assumption is that Dungeon Fantasy is a slightly adversarial game. He's built dungeons and random encounters that are intended to kill the delvers; the delvers are trying to break the encounters. The odds should favor the delvers, but sloppy or careless play will get people killed, maimed, or otherwise rendered useless. Everyone rolls their dice in the open. There are plenty of ways to get rerolls, from spending CPs to Luck to various magic spells. However, if you've used up those resources and a bad roll still gets to you, don't expect the GM to intervene.