I want to speak to an important question, though: why DO we continue? This is a discussion of the rational justification, independent of brain-chemistry. Hamlet is right for the wrong reasons. These are my beliefs:
The only real reason to continue is because you think that you can contribute, in at least a small way, to the long-term well-being of humanity. You, an individual, are a cell in a vast organism of humanity, and your duty is to find something useful to do. There are many ways to do this, as a (spiritual, physical) healer, as a (artistic, technical) creator, or as a player of (business, political) games (who, by the way, use the output of the first two types in the game).
The "long-term well-being of humanity" itself has many possible expressions. On the largest scale, it means making sure that humanity itself can survive any calamity. That means not only taking care of this planet, making sure that it can sustain life, but it also means reaching and colonizing other places in the solar system and galaxy. Given the incredible work required to build a self-sustaining colony orbiting the Earth (which is the only viable option given our level of technology) maintaining intellectual freedom is paramount. Constructing social/political/economic systems that reward power to those with self-restraint, and engender trust in those who could harm us is also important. On a smaller scale, raising children is crucially important, because the organism of humanity needs new cells to replace the cells that die.
Comedians like Stephen Fry are our philosophers. They perform a remarkable feat of alchemy, taking the banal horrors of political and social life and transmuting them in to something funny, something insightful, something that makes you think. Humor is an effective coping mechanism when we face our own prejudices, our own contradictions and, importantly, the same mistakes we see in others. Too often our leaders, and indeed we ourselves, don't laugh enough at the tragedies of our age - for laughter is more powerful than hate, because it criticizes injustice but mercifully leaves behind the terrible burning that anger creates.
Please, Stephen, continue.