Origin
This proverb was first stated in 1791.
Explanation
People will remember the way you appear when you first meet them, so it is important to look and act your best when you meet someone for the first time. Sometimes, we might misunderstand a person. We can’t judge a person just by looking at him/her once. There are lots of girls and boys who fight initially but later become best of friends. But, this proverb is true in case of interviews. A person who apeears confident and capable enough will surely stand a better chance in grabbing that job to a person who looks confused and irresponsible. We may have met a person many times since our first meeting, but his or her appearance as it struck us then is the one that lingers longest in our minds. It means that the first time you meet/see someone, you begin to form opinions based on personal experience.
Example
George spent two hours picking just the right clothes to wear when he met the head of the law firm, since he knew that first impressions are the most lasting.