Despite the mind-boggling size of the universe, the gaps between galaxies are actually fairly easy to comprehend, relative to the size of galaxies. The gaps between stars are much harder to wrap our heads around, relative to the size of solar systems.
Many galaxies are about 100,000 light years wide. The distance to its nearest neighbours is usually only a few to several multiples of that, like continents separated by particularly big oceans. In other words, if you can visualize a galaxy, it’s easy to visualize how close it is to lots of other nearby galaxies. The gaps between galaxies can be measured on the same scale or put on the same map as the galaxies themselves.
Solar systems, on the other hand, are usually only several light hours across (if you stop at the outermost planet), and the distance to the next solar system is a huge multiple of that. So once you’ve managed to visualize the size of a solar system somehow… you cannot easily visualize the distance to the next solar system. It’s crazy bigger. You cannot use the same ruler.
So solar systems are much more isolated on the interstellar scale than galaxies are on the intergalactic scale. Which is weird and cool. #stuffIthinkabout