Habitable planets are very common.  Most stars of approximately the right temperature have them.  Plants.  Animals.  Humans can eat them all.  They have the right nutrients.  We almost never need to resort to terraforming.  It’s a mystery.  Humanity expected a cold and alien universe, full of alien worlds.  Instead we found a universe full of warm and comfortable worlds.  It’s one of the more interesting mysteries of our time.  Why?