Michie, van Stralen & West, 2011. Behavior happens only when Capability, Opportunity, and Motivation are all present at once.
Remove any one component and the behavior doesn't happen, no matter how strong the other two are.
The capacity to perform the behavior, physically and mentally.
Physical skill, strength, stamina to carry out the action.
Knowledge, cognitive skill, comprehension, reasoning capacity.
External factors that make the behavior possible.
Time, resources, location, cues, physical access.
Cultural norms, social cues, what others do or expect.
Internal processes that direct and energize behavior.
Conscious intentions, goals, plans, beliefs about worth.
Habits, emotional reactions, impulses, desires below conscious thought.
Whichever question gets a "no" tells you where the barrier sits. COM-B maps directly to the Behavior Change Wheel's 9 intervention types and 7 policy categories.
If a nudge isn't landing, this is the fastest way to diagnose whether it's a skill gap, an access gap, or a will gap, instead of defaulting to "motivation" every time.