A man is certain he should quit smoking, wants to, and believes it would help. He has not tried. Which belief is the Theory of Planned Behavior still waiting on?

B. Perceived behavioural control, whether he thinks he actually could

Wanting and being able are separate inputs, and intention needs both. Someone who has failed to quit four times may hold a perfect attitude and near-zero perceived control, which is why interventions that only raise motivation keep missing this person entirely.