Sizing People Up: A Veteran FBI Agent’s User Manual for Behavior Prediction: Summary & Key Insights

At the heart of predicting anyone’s behavior lies a single concept: understanding motivation. People are not random. Every action they take, every opinion they hold, flows from what they want most in that moment. During my years in counterintelligence, I realized that when we misjudge someone, it’s rarely because they hid their motives—it’s because we failed to see which motives were truly driving them.

If we want to evaluate reliability, we must begin with empathy, not suspicion. Every person operates within an internal hierarchy of priorities—family, achievement, status, belonging, security, autonomy. When we see the world through their priorities, behavior begins to make sense. A colleague who resists collaboration may not be selfish; he might simply prioritize independence over group success. A partner who’s inconsistent may not lack loyalty; she may prioritize personal growth over stability. To predict what someone will do next, we have to understand what matters most to them and how firmly those priorities are held.

This foundation also teaches humility. People change, and so their motivations can shift under pressure. The credible predictor is not one who assumes permanence but one who continually adapts their understanding as new information arises. In the FBI, I learned that even the most reliable asset could become unpredictable when faced with fear or opportunity. That’s why behavior prediction demands constant observation and deep curiosity—not judgment. When you learn to ask, 'What matters most to this person right now?' you’ve already begun to see the future of their choices.

Over time, I distilled the art of predicting people down to six indicators. Each reveals a core dimension of trustworthiness and human reliability. These indicators are not psychological tricks—they’re behavioral lenses that help you interpret patterns consistently. They are Priorities, Stability, Flexibility, Gratitude, Connectivity, and Self-Image.

Together, these six form a roadmap. When you learn to read them, you can assess not just whether someone can be trusted, but precisely how far that trust extends and under what conditions it might fail. In every setting—negotiation tables, team environments, or intimate relationships—these indicators allow you to navigate uncertainty with insight rather than instinct.