First impressions are essential in our relationships with others. After all, we are social creatures that live in a society in which the people that you know can either help you get "to the top" or crush you, depending on their impression of you. Because of this, much in our lives depends on the positive relationships we have with others.
The following is a quote from page 108 of Miller and Perlman's Intimate Relationships, Fifth Edition textbook:
We start judging people from the moment we meet them. And by "moment", we mean the first twenty-fifth of a second. That's all it takes - only 39 milliseconds - for us to determine whether a stranger's face looks angry (Bar et al., 2006). After more patient deliberation lasting one-tenth of a second, we have formed judgments of a stranger's attractiveness, likeability, and trustworthiness that are the same as those we hold after a minute's careful inspection of the person's face (Willis & Todorov, 2006). Then, after watching the stranger chat with someone of the other sex for only 5 seconds, we've already decided how extroverted, conscientious, and intelligent he or she is (Carney et al., 2007). We jump to conclusions very, very quickly.
It's worth thinking about. Is the impression that others get from you the one that you wish to portray?