Assessing Factors
To assess effect level, first start with your gut feeling, given this situation. Then, if needed, assess three factors that may modify the effect level: potency, scale, and quality. If the PC has an advantage in a given factor, consider a higher effect level. If they have a disadvantage, consider a reduced effect level.
Potency
The potency factor considers particular weaknesses, taking extra time or a bigger risk, or the influence of arcane powers. Holy power is potent against the undead. The supernatural powers of a ghost are potent against a human. An infiltrator is more potent if all the lights are extinguished and they move about in the dark.
Quality/Tier
Quality represents the effectiveness of tools, weapons, or other resources, usually summarised by Tier. Fine items count as +1 bonus in quality, stacking with Tier.
Jex is picking the lock to a Mabinogi safehouse. His party is Tier I and he has fine lockpicks, so he’s effectively Tier II. The Mabinogi are Tier III. Jex is outclassed in quality, so his effect will be limited on the lock.
Scale
Scale represents the number of opponents, size of an area covered, scope of influence, etc. Larger scale can be an advantage or disadvantage depending on the situation. In battle, more people are better. When infiltrating, more people are a hindrance.
When considering factors, effect level might be reduced below limited, resulting in zero effect, or increased beyond great, resulting in an extreme effect.
If a PC special ability gives “+1 effect,” it comes into play after the GM has assessed the effect level. For example, if you ended up with zero effect, the +1 effect bonus from your Warrior’s Bodyguard ability would bump them up to limited effect.
Also, remember that a PC can push themselves (take 2 stress) to get +1 effect on their action.
For a master table of factor examples, see Magnitude. Every factor won’t always apply to every situation. You don’t have to do an exact accounting every time, either. Use the factors to help you make a stronger judgment call, but don’t feel beholden to them.