When you start looking at the Universe, you realize that there are more signals out there than are simply generated by stars. On the one hand, you have astrophysical objects like gas, dust, plasma, as well as stellar corpses and their remnants. But there are also failed stars that didn’t quite make it to the nuclear fusion stage that defines our Sun and the other stars like it: brown dwarfs.
Beyond that, there may also be signatures of planets like Earth out there: planets inhabited by an intelligent civilization. It’s of paramount importance, when asking the biggest questions, to make sure that we aren’t fooling ourselves, but that’s where projects like SETI and Breakthrough Listen come in: to help us extract legitimate science where “wishful thinking” has the potential to lead us in precisely the most dangerous direction: the possibility of fooling ourselves.