When we say someone has someone pegged, we mean that the person has correctly identified the qualities, behavior, or intentions of the other person. Some synonyms for this phrase include, "figured out," "decoded," "cracked the code," "gotten a handle on," "mastered," and "read like a book." It is often used to refer to situations where someone has made a correct assessment of another person's character, skills, or motives. Having someone pegged can be a useful skill in situations such as negotiations, business dealings, or personal relationships. The ability to understand the other person's psychology and motivations can be of great value in achieving one's goals and building successful relationships.