People.

Some people come into your life, and make it better. Others, make it worse.
Some people, when they walk out of your life, leave a little hole in the fabric of your life, which no matter how many new people you meet, can never be repaired. Others walk out, and you hardly notice the difference.
Some people make you wonder, an year after you lose touch with them, if you should have tried harder to stay in contact. Maybe they were worth the extra effort. Others, despite the extra effort on your part, cannot be bothered, so you let them go, after a while.
Some people make you wonder, 10 years down the line, what they must be doing now and what they must have become by now. And you wish them well in what they're doing.
Sometimes, when you do re-contact someone after a very long time, it gives you a sense of joy. And sometimes, you also realize that it was okay to let them go when you did.
But no matter how long or how short the time you know them, no matter how much or how little you like them, each one of those people affects you, most of the times in unrecognizable ways. Some make you a better person just by opening up to you, others force you to become a better person by being the worse one themselves, others just make the ride more worthwhile and pleasurable. Isn't that what it's all about, making the most of it while we're here?