People who are guarded in their interactions and tend to be reserved in revealing personal information are referred to as:

Individuals who are guarded in their interactions and reserved in sharing personal information fit best into the category referred to as "Thinkers." This personality type is often characterized by a preference for analysis, reflection, and a cautious approach to emotional expression. Thinkers tend to prioritize logic and reasoning over emotional engagement, which can lead to them being more reserved and selective about what they choose to share with others.

In contrast, the other personality types would have different tendencies. Achievers are typically characterized by a goal-oriented and proactive approach, often more open and confident in sharing their experiences and accomplishments. Relaters are generally more open and communicative, valuing personal connections and being more comfortable expressing their feelings. Sellers are often outgoing and persuasive, thriving on interaction and the sharing of personal stories to connect with others. Thus, the reserved and guarded nature aligns most closely with the traits associated with Thinkers.