This is supposed to be some great secret, isn't it? Something complex and impossible to understand with our feeble minds. Really, it's very simple, and once you fully grasp it, very uplifting. In fact, it is even the most basic - and important - teaching of almost every religion.
Here it is: We are here not to serve ourselves, but to help everybody else. Yeah, that's it. Think of others before you think of yourself, and you will be a better and happier person. Sounds simplistic? Too easy? It is! Altruism is a natural tendency of human beings. Just make your contribution to the world, and help make it a better place. Why is this important? Each individual can make a difference, no matter how small. More importantly, given the numbers of people in this world, good deeds quickly add up.
Another natural tendancy, selfishness, must be overcome. The selfish people of the world end up doing more harm than good. They tend to step on others to get what they want. Eventually, they are shunned or even punished for this behavior. Those who don't learn to work with people always tend to be alone and lonely, lead a shorter life, or end up locked away so they can't do any more damage. To risk sounding a little cliche, evil always loses, as evil has no friends, only enemies. With no friends to be there to help, the increasing number of enemies will eventually become overpowering. Being self-serving ultimately requires a lot of work, and is very difficult to sustain.
Helping others is more rewarding in the long run than helping yourself. Why? Because others will learn that you are a good person, and will go out of their way in turn to help you when you need it. This might sound obvious or sappy, but there's no other way of putting it. We must help each other first.
To make a point, I'm going to commit a Zen no-no, and answer a couple of Zen puzzles. This is not supposed to be done, because you are supposed to find the answers on your own. There are hundreds of these questions, so answering a couple shouldn't hurt. These two are so most often heard that they're almost cliche.
What is the sound of one hand clapping? It's the sound of nothing. That's obvious enough, but there more to it than that. It is the sound of failure because one hand is refusing to work with the other. You need two hands to make a clapping sound.
We all need each other to survive and improve. Nobody can survive effectively in this world alone. Sure, there are the few hermits, but what have they done for this world? If they have done anything, how will anybody know of their deeds? Communication and the ability to work together are the most important skills a person can have.
If a tree falls in the forest, and no one is there to hear it, does it still make a sound?. Ok, here's another one that I'm going to answer, even though I'm not supposed to. (No, it isn't about sound waves and physics. That's not the point of the question!) It's a trick question, but aren't they all? The forest is there to hear the falling tree, and every single living thing nearby is immediately affected by that tree falling. Even if there are no human beings around it, that tree will eventually have some effect on all of our lives.
For example, say the noise startles a squirrel, who runs off and happens not to end up becoming a fox's lunch. Instead the fox works extra hard to chase down a rabbit, who is no longer around to eat a certain gardener's plants. This gardener goes to a day job more cheerful, and works harder to solve a major problem for the corporation. That corporation doesn't go bankrupt, which in turn doesn't tip the economy into recession. This is just a hypothetical example, and it may be a bit extreme, but you see how a small thing can escalate to make a big difference. There are no "what if's". It will have an effect in one way or another. We all hear that tree fall in one major way or another minor one. Everything is connected.
What's my point? The point is that we, as a society, are going somewhere. We are growing and advancing. Our social and technological advancement is accelerating, faster and faster. Advancements are coming logarithmically, as we use the knowledge we find and the advancements we make to gain more knowledge and make more advancements. As advancements are made, each individual gains more power to add to this growth. Every little bit of knowledge adds up exponentially as it spreads from person to person. The collective group can do great things!
Look at the explosion of web sites (like this one) out there. The fact that you are reading this means that this particular individual is having an effect. You may take something you picked up here and apply it to your own life, and affect others' as well. Sure, it may be a small thing, but if some people become less self-centered because of this web page, that means the world is a better place to live in. One more altruistic person will help others, who will come to the aid of still more people...
The end result is that our society will continue to grow in complexity and sophistication. We will develop the tools to handle this, and we will always want to improve using these tools. Look how far we have come! Imagine where we are going! We need your help! Every single individual is very important. This is what it all means.