A lot has to do with age and exposure. Both elementary school and High School provide a much smaller group of people that one can learn to navigate around over many years. This is a much more "intimate" world in that it's actually smaller as opposed to what is out there on a much bigger scale that is not so small and intimate anymore. Actually grammar school and high school is much like the safer places young fish grow up in meant to give them more safety and a better chance to grow and thrive, but as young fish grow and get bigger they have to move out to the bigger seas where they no longer that the same kind of protection they did in the safer smaller environments. Truth is that even popular kids find out that once they leave that smaller world of grammer school and high school, they are in a whole new bigger world where they have to find their way in a big sea of people than what they are used to. It's always a big adjustment because it's simply a much bigger world than what anyone is used to that finally leaves the grammar school and high school smaller world. So you are not alone in experiencing these challenging feelings you are experiencing.