We know the odds of evolution are low; the point is that the number of stars in the Universe is astoundingly huge. With at least 10^20 stars in the Universe, those low odds get much more reasonable, especially now it's starting to look like planets are common.
Do you know the actual odds, though? I mean, there's low and then there's low.
If evolution on a habitable planet has a 10^-4 chance of happening, then the universe is almost certainly teeming with life. If it's 10^-18, the size of the universe is the difference between believing and doubting the idea. If it's 10^-200, the universe barely helps at all, and you need to start talking about billions upon billions of barren universes and we just happen to live in this one.
Do you know what the number is? Do you know where it lies between 0.9 and 10^-(10^10^10)? Do you know whether the 20 orders of magnitude you get from the stars is overwhelming, decisive, or not even enough to make a dent?
To my way of thinking, the fact that life showed up on Earth relatively quickly, within half a billion years of the planet's formation, suggests that life is relatively easy. The fact that complex life took another few billion years after that suggests that simple to complex is the difficult step. But the fact that we nonetheless find ourselves here around a live-fast-die-young yellow star when the universe is only 14 billion years old rather than in close orbit around a dim red star a hundred billion years later suggests to me that it's probably not a one-in-every-zillion universes sort of event.
