(Thanks to hickerphoto.com for the image!)
Leaving an imprint in the sand is the same as leaving an impression on a person. The stronger you let down, the deeper the impression.
After a long period of time, meeting someone again (even though you may know this person very well) can get you nervous. Nervous for the fact that you may have changed since you both last met. From appearances to personality, a lot can change in a person. Making a second, third, or the hundredth impression will just be as important as the first.
Nonetheless, impressions after the first won't be as tough as the one that introduced who you are. Walking into a job interview in your shorts and casual t-shirt isn't going to get you anywhere. But I just wanted to show my free-spirited personality! After all, people say that I'm too formal and professional sometimes. As great as a professional as you may be, you have plenty of time to show your free-spirited personality after you get the job—that is, if you had left a good first impression on your interviewers.
There are many different individuals in the world, though. Some are completely off the wall, while others are strictly proper. There are many people who don't care about their appearances and impressions at all, in addition to those who are absolutely obsessive about who they are. It's tough to change that.
Not to mention: leaving an embarrassing long-lasting impression. Though you might not know it, someone might still remember you peeing in your pants in first grade (yes...something as embarrassing as that will stay with people forever), or you getting drunk at a party and admitting that you can't sleep without a nightlight.
"Stride – The Ridiculously Long-Lasting Gum!" <--Yeah, leave a good impression as long-lasting as that...well, maybe not that long.