Understand the action line — the threshold where behavior fires

Every behavior has a required minimum of motivation × ability; staying above that action line is the design goal.

Why it works

The Fogg model positions behaviors on a curve: high motivation can compensate for lower ability, and vice versa. The "action line" is the threshold that must be crossed for a behavior to occur given a prompt. The key design insight is that lowering difficulty moves the action line down — making it easier to cross even when motivation is low — which is far more controllable than raising motivation.

How to do it

1. When a behavior fails to fire, map it: Was motivation below your typical range, or was the task harder than usual?
2. If it’s a motivation problem, address the prompt and motivation context; if it’s ability, reduce the task.
3. Try reducing the behavior difficulty until it reliably fires even on hard days — that’s the correct floor.
4. Consciously distinguish between "I don’t want to" and "I can’t right now" — they need different solutions.

Evidence

The action line concept formalizes the multiplicative relationship between motivation and ability that is implied by expectancy-value theory and consistent with behavioral research showing that both factors must reach sufficient threshold for action. This is a practitioner formalization of established theory. (mechanistic)

The specific action line curve is a model for intuition and diagnosis, not a precisely measured construct. The underlying idea that motivation and ability trade off is supported by theory but the graphical formulation is not independently validated.

Common mistake

Treating motivation and ability as fixed when they are both state-dependent — the action line changes daily, which means a behavior that fires reliably Monday may fail Friday without any change in will or commitment.