Do you believe that your first impressions are accurate? What we consider a "first impression" is our mind's way of categorizing people, objects, ideas, and situations using as little cognitive energy as possible. In psychology, these processes are often referred to as heuristics or schemas and have an evolutionary explanation. In somewhat simple terms, we have adapted a system that is best suited for forming impressions that increase our chances for survival. This means that accuracy of these cognitive processes is not the main concern—survival is, which leads to something called false positives, better known as "false alarms."
This survival mechanism comes with a price tag that leads to stereotyping, prejudice, irrationality, being unreasonable, and inaccuracy in our judgments. Critical thinking requires that we don't always take the shortcut, but invest the mental effort to avoid these costs. Admittedly, this exercise is a blow to the ego for all those people who believe they are "highly intuitive" because they remember the times they were right but conveniently forget all the times they were wrong.
We are presented with too much information to update all impressions with critical thinking, but the more we practice, the more efficient we will become at determining the accuracy of our first impressions.