I don't think anyone takes size into scope when talking about life in the universe. Meaning; What if some solar systems are actually atoms. Life doesn't have to be carbon based and atoms don't have to be ones we know on the periodic table. Each solar system could be an atom. These atoms could make up a cell in a single cell life form. That is only IF life has to start in the form of a cell like our life started here on earth. It doesn't though. The principle behind this is huge. though. We are looking for life on other planets in our solar system (that could be electrons in an atom) and in other solar systems but we haven't entertained the though that not only could our solar system be an atom, but the atoms that make up our bodies could be solar systems which harbor life of some sort. When you open your mind to this you can see that size is the scope that we are failing to grasp. The universe is unlimited, meaning that it goes forever outward. It could also go inward with an unlimited scope. There may not be a stopping point as far as how small or how large things can be.