But how many factors are they really taking into account? In addition to being at a good distance from the sun, good size, good rotation speed, good chemical composition, and good temperature earth has going for, there are also things like how the moon stabilizes the environment, and Jupiter deters comets and asteroids away from earth. There's probably a few hundred I can name, but you get the idea. Sure, you could say that life works the way it does because of those conditions, but the point is we don't actually have evidence of it being able to work any other way. Not that I wouldn't like the idea of a universe filled with life.