Human brains are wired to form snap judgments, a survival mechanism from our evolutionary past. Research shows we make initial assessments of trustworthiness and competence within 1/10th of a second of meeting someone. These impressions are surprisingly durable, often persisting even when contradicted by later evidence. The phenomenon stems from our brain's tendency to rely on mental shortcuts for efficiency.

Several subtle factors influence these automatic judgments. Voice pitch affects perceived authority, with deeper voices generally rated as more competent. Facial structure plays a role too - people with broader faces are often viewed as more dominant. Even something as simple as wearing glasses can increase perceptions of intelligence by about 14%. Interestingly, these effects show remarkable consistency across cultures, suggesting biological rather than purely social origins.

While first impressions are powerful, they're not unchangeable. Consistent behavior over time can override initial judgments, especially when the later information is strong and repeated. Being aware of these psychological tendencies helps us both in making better first impressions and in avoiding the trap of judging others too quickly based on superficial cues.