There are a few factors here. First the constellations exist, there are stars there in those configurations. read more
There's no need to "believe" in stars -- they're real. There are some 100 billion of them in our galaxy, with the nearest one being about 4.25 light years away, and hundreds of billions of galaxies in the universe. Constellations are simply "patterns" we humans make out of the random appearances of stars in our sky. read more