Circumstances are those situational aspects that influence the probability of success positively (advantage) or negatively (disadvantage). A given circumstance may be an advantage one moment to one character’s action and a disadvantage the next.
Advantages and disadvantages offset each other, with any remainder adding additional dice to the base 3d6 Roll. If the remainder are advantages, pick the best 3 dice of the roll. If the remainder are disadvantages, pick the worst 3 dice of the roll. No more than 7d6 are ever rolled.
You can track circumstances on your character sheet if they are personal, or on an index card or some other shared space with the players at the table.
Circumstances that can influence an action are always applied.
A circumstance can have a duration of once, scene, milestone, adventure, permanent. This is the amount of time that must pass before the circumstance can be overcome.
A circumstance is usually just a 1d6 advantage or aisadvantage. However, some may have degrees of intensity. Darkness is a good example: dim light (1), heavy shadows (2), and pitch black (3). If a Circumstance can be described with degrees of intensity, 3 steps should be the maximum.
Circumstances are italicised with the number of dice to indicate the intensity if greater than 1d6.