Final answer:
The complexity of an attitude and its source are factors that influence our ability to predict behavior from attitudes; more complex attitudes make prediction difficult, while credible sources can make attitudes more predictive of behavior.
Step-by-step explanation:
The factor that influences the probability that we can predict people's behavior from attitudes is the attitude's complexity. Attitudes are comprised of an affective component (feelings), a behavioral component (effect on behavior), and a cognitive component (belief and knowledge). The more complex an attitude is, the harder it may be to predict behavior based on that attitude alone, as complex attitudes might involve conflicting feelings or beliefs that could lead to unpredictability in behavior.
Furthermore, the attitude's source is also influential. If the source of an attitude is perceived as credible and trustworthy, it might be conveyed with more conviction, and therefore, inform behaviors more consistently. Conversely, attitudes stemming from less credible sources may be easily dismissed or may not be deeply held, making behavior prediction more difficult.