This Is About You.
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Consider that your mother and father never met (through, perhaps, some culmination of chance events, or, if you are that way inclined, through the ineffable auspices of a higher power).

You would have never been born.

Then consider that for your parents to meet, fall in love (or not fall in love), concieve a child (or children - if you have a twin), and so forth, four _completely unrelated_ (or related - if you're from Tasmania) people had to have met too.
And for them to meet, eight unrelated people had to meet.
And for those eight people, sixteen men and women who, again, never necessarily knew each other, who may have been from completely different parts of the world, had to meet.
If just one of those people had died, had missed a train, had gotten lost, had slept in, had left home a little early, _you wouldn't be here_.

And that's just going back to your great-great-grandparents. That's possibly still in the twentieth century. That's fiddlesticks compared to all of human history. And every generation you go back, there are more and more people who had to concieve a child so that you could be here reading this.

If you're a creationist Christian (and that's cool - I'm not a Christian, but some of my ancestors were, and if it was through their faith that they met - and since people lived smaller back then and church was a big part of life, that's quite likely - then woe betide me to criticise Christianity), then you can trace back your existence to Adam and Eve. The wellspring of human existence. Adam and Eve lived maybe 5000, maybe 10,000 years ago, according to Young Earth Creationists. Considering that for much of human history, a generation was about 16 years long, that means that for you to be here, between 312 and 625 generations of people - mothers, father, grandmothers, grandfathers, and so on - had to have met. A whole bunch at the beginning - Adam and Eve and their children - we can take for granted, but after that, chances get astronomically high that you wouldn't be you, because somewhere along the track, somebody met somebody else.

If you are friends with science and evolutionary theory, on the other hand - and that's where I sit - then you can trace your existence back to the dawn of life on Earth, some 3.7 billion years ago. That's a really, really long time. The generation age only works for modern, evolved people, as most animals don't wait 16 years to have babies. So, saying roughly that homo sapiens diverged from other hominid species some 200,000 years ago, and that the generation age since that time has been perhaps 13 years, given human physiology, then that means that your existence is the product of 15,380 generations _since humans could be defined as humans_, and millions more before then. Chimps (our closest related species and a good estimate of what our ancestors looked like) reach puberty at around 9. So for the roughly 20 million years that our ancestors resembled chimps, add another _two million_ generations. And so on. For three and a bit billion years.

Of course, there would have been extinctions and evolutionary bottlenecks - times when the population of the species got so low that there was no choice but to mate with the last few remaining members. That doesn't make your existence more of a given. It makes it more unlikely. What if the animals that were supposed to give birth to the animals who would one day become humans were part of the 70% of species which died out in the Permian extinction? Imagine what the world would be like if those 70% hadn't died out. You certainly wouldn't be in it.

Your existence is a profoundly microscopic fluke in a long line of microscopic flukes. You are the product of a lucky sperm and a well-placed egg, created by chance from two people who, themselves, were lucky to be there at the moment of conception.

Your existence is rare and improbable and highly, _highly_ unlikely.

Spend it doing something marvelous.