So I've been in e-mail contact with island, who commented on my second Abusive Cosmology post. I had previously known that Earth is a rare specimen, but I have since gained a much greater appreciation for just how rare our circumstances are here on this pale blue dot.
Earth occupies what is known as a "Goldilocks Zone," a whimsical yet apt term which amounts to walking a knife-edge between competing runaway forces. Uninhabitable extremes characterize the overwhelming majority of the Universe and prevent life from cropping up almost everywhere. However, these opposed runaway forces of extreme heat and cold, crushing gravity and hungry vacuum, as well as others, occasionally strike a balance between them that makes it possible for life as we know it to arise and thrive.
Now, we can imagine Goldilocks Zones for any phenomenon we'd care to dream up, be it life, molten metal, solar flares, factories, or whatever. The simple fact of the matter is that there are just about always more ways for any given thing to not exist than there are ways for it to exist. What's interesting is that these Goldilocks Zones have relevant features at all levels of reality. In terms of life, there is a Goldilocks Zone between Earth's mantle and its ionosphere into which all life has shoe-horned itself. Locally, every organism has its niche, and there are plenty of places on the planet where any organism you'd care to name simply could not survive: no species can survive absolutely anywhere on Earth.
Earth itself is in a Goldilocks Zone relative to our star, Sol: too close and we burn, too far and we freeze. Our solar system itself is a roll of the die that came up "life-friendly," with gas giants sweeping up the riff-raff of cosmic debris (which would otherwise pelt every small rocky world into oblivion), and without so much eccentricity in their orbits as to screw with the inner rocky planets. And the position we occupy in the galaxy is far enough out from the gene-scrambling radiation of the galactic core, but not so far out as to lack the heavier elements needed for more complex life. With respect to time, life cannot come about during the initial or final phases of a planet, star, galaxy, or Universe (at least, not a Universe that starts with a Big Bang and ends with either a Big Crunch or heat death). And with respect to physical laws, they have to be such a way as to allow life to be possible anywhere at all (though whether they could be otherwise is at present an open question).
This preponderance of interesting features reminds me of the Coastline Paradox, which refers to the difficulty of determining the "exact" perimeter of a coastline. You see, coastlines have relevant features at all levels of detail, and these change on all timescales. From biggest to smallest, coastlines have features observable from space that change in geologic time, and features on the more human-appropriate scale of meters that change daily with the tides, and features on the atomic scale that change rapidly all along the progression and recession of every single wave.
So what's the "true" length of a coastline? Ain't none. We can arbitrarily decide which features are important and which are not (the Wikipedia page mentions the appropriately useful tactic of omitting features significantly less than the unit in which the measurement is being made), but no output from any such method has a privileged status over any other. Trying to find the true or exact length of a coastline, even in a snapshot of time, is like trying to find exactly how many grains of sand constitute "a heap."