Luck represents that unexplainable tendency for good things to happen to certain people without their effort or awareness. This is a rule which used to be a part of the core Window mechanics, but has now been relegated to the status of an optional rule. The reasoning behind this is that the luck trait works slightly differently than other traits...
If the Storyteller wants to use luck in her stories, she could add it to the list of traits that all of the cast members must define, or she could allow it as a skill just for specific characters. It works the same in either case.
Luck rolls are called for when chance is all that stands between two paths for the story to take, or immediately after a failed success roll to give a character that one last chance... Another use for luck is to settle minor questions which have little bearing on the story, such as whether a character happens to be wearing a hairpin or carrying a lighter.
Luck can be a character's best friend. If he makes his luck roll he can save himself after a particularly dismal die roll, a feature which allows for a certain heroic confidence when entering dangerous scenes. Luck can also be the Storyteller's best friend. For her, it can be a way to maintain the troupe's sense of hope in hopeless situations, and it provides a good way to solve many minor arguments that arise between her and the actors...
Luck rolls are identical to basic success rolls in how they work: the Storyteller sets a target number and if you roll equal to it or under, you succeed. If no target is specified, you must roll a 6 or less.
By the way, luck can also be called something else if it better
fits the setting. In superheroic roleplaying, for instance, luck
could be called "heroism," since those sorts of characters rely
more on their extraordinary abilities to save them in times of
peril. In a setting which is populated by gods or guided by astrological
forces, the Storyteller could opt to call it "fate."
There comes a scene in a character's life when he's hit bottom, when the situation has become so grave that nothing short of a miracle can save him now. In the Window, the luck trait allows one final recourse to turn the story back into his favor...
If such a case occurs where you've failed a luck roll that was really important, you may at that moment choose to "trade" some of your permanent luck to change the roll to a success. This choice causes your luck trait to drop a permanent rung on the competency ladder, but at least your character is still alive and kicking.
Trading your luck in this way can keep your character alive and
on top of things for quite a while, but remember, everyone's luck
has to run out sometime...
Luck Roll Example:
The Ogrean were everywhere. Laerd continued hacking into the fray as he watched Ryla cross the perilous catwalk to safety. "I'm going to run across as fast as I can," he said.
"That's not so easy, Laerd," warned the Storyteller. "Make an agility save, target of 3." Laerd was in the militia and had great balance (D8). He spun and dashed across the beam. The die was tossed: a 7.
"Aye!!" Laerd's foot came out from under him. Ryla screamed as she watched him fall and splash into the freezing water below...
"Make a luck save, Laerd," said the Storyteller ominously, "and you better not miss this one..."
He hit the water hard. He felt the icy embrace as he was swept along. At least he was a little more lucky than the average person (D10).
He rolled: a 7. A target hadn't been specified, so he needed a 6 or less...
The Storyteller raised an eyebrow. "The cold is sapping your strength. From above and behind you think you hear Ryla screaming your name. You fight madly with the waves, but the rushing stream is so painfully cold. You gasp in water... you try to cough..."
"Okay, okay. I'm gonna trade a luck rung," said Laerd defeatedly.
"Alright," responded the Storyteller, "your hand reaches out of the water and catches on a rock. Laerd, your luck is now down to average (D12)."
Laerd climbed coughing onto the shore, then collapsed, exhausted.