Everyone takes turns to alternately write something fortunate or unfortunate about the situation described by the previous poster.
For example:
START: I woke up in the morning and cracked my head open on the ceiling.
Person A: Fortunately, your father is a doctor, and he patches you up.
Person B: Unfortunately, the bandages are pink, making you look like a pansy.
Person C: Fortunately, you are a pansy, etc.
So, for the starting statement:
You are cornered in a dark alley by a knife-wielding maniac.
Fortunately, you have your trusty lightsaber.
For example:
START: I woke up in the morning and cracked my head open on the ceiling.
Person A: Fortunately, your father is a doctor, and he patches you up.
Person B: Unfortunately, the bandages are pink, making you look like a pansy.
Person C: Fortunately, you are a pansy, etc.
So, for the starting statement:
You are cornered in a dark alley by a knife-wielding maniac.
Fortunately, you have your trusty lightsaber.