You have really bad luck. Things just go wrong for you, and usually when you most need them to go right. Once per game session, the GM will arbitrarily and maliciously make something go wrong for you. You will miss a vital die roll, or the enemy will (against all odds) show up at the worst time. If the plot calls for something bad to happen, it will happen to you. You may not be killed outright with bad luck, but anything less is fine. This is not contradictory with the advantage Luck, and you may have both.