A man crosses a swaying bridge, meets an interviewer, and later describes himself as strongly attracted to her. Order the steps two-factor theory says produced that feeling.

1. The bridge sways and his heart rate, breathing and palms all react.
2. The arousal itself carries no label: it could be fear, excitement, or attraction.
3. He scans the situation for what is causing it.
4. The most salient candidate present is an attractive person talking to him.
5. He experiences the arousal as attraction and acts on it later.

Step two is where the whole theory lives. Schachter and Singer's claim is that physiological arousal is emotionally ambiguous - a pounding heart is a quantity, not a feeling - and it is the cognitive appraisal of the situation that determines which emotion is experienced. Change what is salient in the environment and the same arousal becomes a different emotion.

That is what makes misattribution possible, and misattribution is the theory's most testable prediction. A man on a solid bridge has no arousal to explain and reports ordinary interest; the man on the swaying bridge has arousal that the bridge could account for and attributes it to the person instead.

It is worth noting where the theory has been challenged. Some arousal states appear to be more physiologically distinct than the theory allows, and the original Schachter-Singer experiment has replicated inconsistently. What has survived robustly is the narrower claim: arousal from one source can be transferred to another and intensify whatever emotion the situation suggests.