Final answer:
Motivation is the key predictor of whether individuals will change their substance use behavior.
Step-by-step explanation:
The key predictor of whether individuals will change their substance use behavior is motivation. Motivation refers to the internal or external factors that drive a person to engage in a certain behavior. In the context of substance use, individuals who are motivated to change their behavior are more likely to seek help, attend therapy, or engage in other interventions to address their substance use.