The End to all Means

  I say this with almost no doubt; happiness is the absence of suffering. Yes, pleasures can be enjoyed, but fundamentally, being rid of discomfort is what we truly want.
  However, we don't always act in accordance with this. We're not very efficient, in body and mind. No life is. Emotion makes things difficult. Emotion makes us do silly things. We eat unhealthy food. We hate people. We spend all our money on booze, and other such things. We may want happiness, but our subconscious mind does a shitty job of getting it for us. But considering the theory of evolution, that can be explained. If satisfied, we stop striving, meaning we do not eat, drink, reproduce, or do things that facilitate those 3 things. That is, unless we have reason.
  Reason is key. Where emotions drive us to do all these foolish things, reason has undone its mistakes time and time again. Reason takes in the input of the senses and turns it into action toward the goal it has been given. Action which succeeds. You see that being cold is suffering, and being warm means being free of that suffering. We realise clothes keep us warm - so we create clothes. This is but one, fairly mundane example of when reason has helped us. Now of course, our emotions can use reason for its own ends. Some people have applied reason so that you can get tasty food at McDonald's all over the world, even though it's bad for you. But if we apply reason to the lessening of suffering as a whole, regardless of what we do or do not feel, we can significantly reduce that suffering.
  Notice, though, that I say 'suffering as a whole'. I'm not just talking about a personal freedom from suffering. I'm talking about suffering full stop, regardless of what sentient being it might occur in.
One of the scariest questions to be acknowledged is "Why help anybody else? Why not just shit on them for my own pleasure (or in this case, freedom from suffering)?". My answer isn't so scary. To illustrate, I will explain how I came to the conclusion I have.
First, I asked the questions. "Why worry about others' suffering?" and then "Why worry about my own suffering?". Both positions, selfishness and altruism, seemed arbitrary. There seemed to be no reason to accept either. But then I remember that to make the distinction between self and other is entirely arbitrary. If you stop thinking "I work for myself" and look at things completely objectively, stepping out of your 1st person perspective and take a 3rd person perspective. there is no reason to prioritise your suffering above anybody else's, just because it's happening in that place you call "I" or "me". If there is no reason to do something (in this case, 'make a distinction'), then we do not do it.
This does not mean you have an obligation to go out and help all 7 billion people in this world. That's impossible. But what IS possible? The Stoics helped me answer this question.
To conclude. though, I must admit something. I can give no reason why we should avoid suffering. But that's probably why I think it's the basis of all action, and only a direct experience of it is sufficient to truly understand it. At least, for now I think so.