Life as we know it - and this is a key way of phrasing it - depends on a whole lot of things being true. It depends on having plenty of carbon and water (and a whole slew of other elements) available, it depends on our planet being just the right distance from the sun (too close and we burn up, too far away and everything is a frozen wasteland), it depends on our planet being roughly the size it is lest the gravity is too overwhelming to make moving around difficult, or so light that our atmosphere wouldn't stick around. It's also dependent on water being at its heaviest at 4 degrees celsius or our lakes would freeze from the bottom up. We likely have the gigantic Jupiter to thank for not having more comets and other Big Objects that hurl through space crashing into us and wiping us out. Our planet's iron core creates a magnetic field that is believed to stave off the worst of cosmic radiation that had otherwise wiped us out. It's a stroke of luck too, of course, that DNA is just the kind of molecule that replicates itself with very high fidelity but not too high so that we can mutate often enough for natural selection to actually pull off the amazing feat of producing Life As We Know It. And let's not forget that conditions on our planet 4 billion years ago had to be just right in order for the first self-replicating molecule to appear at all.
Our Cosmic Goldilock's List of Requirements could be made very, very long and could be made to include the basic properties of our solar system (for instance the fact that the Sun is a "young" star is what gives us the heavier elements of which we are composed; it takes a star made out of exploding earlier stars to achieve that) and even the very constants of the universe, including the speed of light, the strength of the known forces (Electromagnetic, Gravitational, Strong and Weak respectively). In short, it all seems very delicately calibrated to create life on planet earth and eventually humans. One explanation for this happy coincidence is to invoke a deity (or deities, depending on your preference), and that's understandable - it's a bit ridiculous to expect everything to match our needs so intimately just by sheer coincidence. But, to me, thereal answer is not just a more powerful explanation of the circumstances but also beautiful in its simplicity:
We're here to marvel at just how perfectly the universe in general and our world in particular fits us specifically because if it hadn't, we wouldn't have been. We couldn't have been here to grudgingly complain about how poorly the world suits us because we wouldn't be in a world that suits us poorly. We're like a puddle of water gasping in awe over how amazingly well the hole we reside in fits us when in reality it's the hole that dictates our shape.
In a universe or a world that was very different from the one we're in or on now, it's likely that there wouldn't be life at all. But if there were and that life evolved intelligence and science, they, too, would marvel at how incredible and unlikely it was that they should wake up in a universe that happened to fit them so well in everything from how atoms (or their corresponding basic particles; who knows how the laws of physics would work where they would live) were constructed all the way up to how lucky they were to live on a planet that was 2000 degrees in the day because without the massive heat they wouldn't survive.
That, in a nutshell, is the anthropic principle. You can read more about it on Wikipedia: http://en.wikipedia.org/wiki/Anthropic_principle
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