People often use mental shortcuts to form impressions of other people. For example, social categorization involves sorting people into different groups based on common characteristics. While this is a natural process that allows you to make decisions and judgments quickly, it can lead to very inaccurate impressions of those around you.
While first impressions are indeed important, additional information that you receive after the initial impression can change what you think about and how you behave around a particular person. Using the primacy effect, you can determine how much of an impact first impressions have on you and how much they influence any new information you might receive. Primacy effect is the tendency for initial information to carry more weight than information received later (also, in memory experiments, the tendency for initial words in a list to be recalled more readily than later words).
As seen in A. S. Luchins's The Order of Presentation in Persuasion (1957), the following paragraph was used in an experiment to determine if the primacy effect was apparent in people's assessment of what kind of person “Jim” was:
Jim left the house to get some stationery. He walked out into the sunfilled street with two of his friends, basking in the sun as he walked. Jim entered the stationery store, which was full of people. Jim talked with an acquaintance while he waited to catch the clerk's eye. On his way out, he stopped to chat with a school friend who was just coming into the store. Leaving the store, he walked toward the school. On his way he met the girl to whom he had been introduced the night before. They talked for a short while, and then Jim left for school. After school, Jim left the classroom alone. Leaving the school, he started on his long walk home. The street was brilliantly filled with sunshine. Jim walked down the street on the shady side. Coming down the street toward him, he saw the pretty girl whom he had met on the previous evening. Jim crossed the street and entered a candy store. The store was crowded with students, and he noticed a few familiar faces. Jim waited quietly until he caught the counterman's eye and then gave his order. Taking his drink, he sat down at a side table. When he had finished with his drink he went home.
The description, when split in half, describes Jim in two different ways. Up until the sentence that begins “After school, Jim left …,” Jim is friendly and outgoing. After that point, he's described as a shy, introverted, and unfriendly person. Of the people who read only the first half of the description, 95 percent thought him to be friendly, whereas of the people who read only the last half of the description, 3 percent thought him to be friendly. What's interesting is that of the people who read the entire description with the “unfriendly Jim” description first, only 18 percent thought him to be friendly. This shows that our initial impression of a person has the most significance in our general opinion of a person.